Extended Layout Architect – how can I find the site source code?

If you are working with the advanced layout builder – the site structure is build with shortcodes. Each Element has its own shortcode.
You can see the whole site shortcode if you activate the debug mode.
Put this to your functions.php of your child-theme:

add_action('avia_builder_mode', 'builder_set_debug');
function builder_set_debug(){
  return 'debug';
}

after that you will have under the editor fiele an additional field with the shortcodes f.e.:

the whole code can be copied and on a new created page in advanced layout builder mode pasted into that field – then save the page and the alb on top will show the layout structure then.

no the whole code – try yourself – this is one of my pages:
https://webers-testseite.de/3columns/

[av_section min_height='' min_height_pc='25' min_height_px='500px' padding='default' margin='' custom_margin='0px' color='main_color' background='bg_color' custom_bg='' background_gradient_color1='' background_gradient_color2='' background_gradient_direction='vertical' src='' attach='scroll' position='top left' repeat='no-repeat' video='' video_ratio='16:9' video_mobile_disabled='' overlay_enable='' overlay_opacity='0.5' overlay_color='' overlay_pattern='' overlay_custom_pattern='' shadow='no-border-styling' bottom_border='no-border-styling' bottom_border_diagonal_color='#333333' bottom_border_diagonal_direction='scroll' bottom_border_style='scroll' scroll_down='' custom_arrow_bg='' av-desktop-hide='' av-medium-hide='' av-small-hide='' av-mini-hide='' id='' custom_class='' aria_label='' av_element_hidden_in_editor='0' av_uid='av-39o199']
[av_heading heading='Flex Box Model with 1/3 Columns' tag='h2' style='blockquote modern-quote' subheading_active='subheading_below' size='36' av-medium-font-size-title='' av-small-font-size-title='' av-mini-font-size-title='' subheading_size='24' av-medium-font-size='' av-small-font-size='' av-mini-font-size='' color='' custom_font='' margin='' margin_sync='true' padding='10' link='' link_target='' id='' custom_class='' av_uid='av-kbi07d5u' admin_preview_bg='']
one color-section with custom-class:   <strong>custom-css</strong> - or what ever you like.

only your 3 columns in this color-section no other elements in it!

columns on individual height !
[/av_heading]
[/av_section]

[av_section min_height='' min_height_pc='25' min_height_px='500px' padding='default' custom_margin='0px' custom_margin_sync='true' color='main_color' background='bg_color' custom_bg='#e8e8e8' background_gradient_color1='' background_gradient_color2='' background_gradient_direction='vertical' src='' attachment='' attachment_size='' attach='scroll' position='top left' repeat='no-repeat' video='' video_ratio='16:9' overlay_opacity='0.5' overlay_color='' overlay_pattern='' overlay_custom_pattern='' shadow='no-border-styling' bottom_border='no-border-styling' bottom_border_diagonal_color='#333333' bottom_border_diagonal_direction='' bottom_border_style='' custom_arrow_bg='' id='' custom_class='custom-css' aria_label='' av_element_hidden_in_editor='0' av_uid='av-b33mwt']
[av_one_third first min_height='' vertical_alignment='av-align-top' space='' row_boxshadow_color='' row_boxshadow_width='10' margin='0px' margin_sync='true' mobile_breaking='' border='' border_color='' radius='0px' radius_sync='true' padding='30px' padding_sync='true' column_boxshadow_color='' column_boxshadow_width='10' background='bg_color' background_color='rgba(176,43,44,0.3)' background_gradient_color1='' background_gradient_color2='' background_gradient_direction='vertical' src='' attachment='' attachment_size='' background_position='top left' background_repeat='no-repeat' highlight_size='1.1' animation='' link='' linktarget='' link_hover='' title_attr='' alt_attr='' mobile_display='' id='' custom_class='' aria_label='' av_uid='av-k3unnj4d']

[av_heading heading='Column1' tag='h2' link='manually,http://' link_target='' style='blockquote modern-quote modern-centered' size='' subheading_active='' subheading_size='15' margin='' padding='10' color='' custom_font='' custom_class='' id='' admin_preview_bg='' av-desktop-hide='' av-medium-hide='' av-small-hide='' av-mini-hide='' av-medium-font-size-title='' av-small-font-size-title='' av-mini-font-size-title='' av-medium-font-size='' av-small-font-size='' av-mini-font-size='' av_uid='av-1q98xr1'][/av_heading]

[av_textblock size='' font_color='' color='' av-medium-font-size='' av-small-font-size='' av-mini-font-size='' id='' custom_class='' av_uid='av-k3unomjx' admin_preview_bg='']
<strong>Ich bin der Geist, der stets verneint!
Und das mit Recht; denn alles, was entsteht,
</strong>
[/av_textblock]

[av_button label='Click me' icon_select='yes' icon='ue800' font='entypo-fontello' size='small' position='center' label_display='' title_attr='' color='theme-color' custom_bg='#444444' custom_font='#ffffff' link='manually,http://' link_target='' id='' custom_class='' av_uid='av-ka5b3zfy' admin_preview_bg='']

[/av_one_third][av_one_third min_height='' vertical_alignment='av-align-top' space='' row_boxshadow_color='' row_boxshadow_width='10' margin='0px' margin_sync='true' mobile_breaking='' border='' border_color='' radius='0px' radius_sync='true' padding='30px' padding_sync='true' column_boxshadow_color='' column_boxshadow_width='10' background='bg_color' background_color='rgba(237,174,68,0.3)' background_gradient_color1='' background_gradient_color2='' background_gradient_direction='vertical' src='' attachment='' attachment_size='' background_position='top left' background_repeat='no-repeat' highlight_size='1.1' animation='' link='' linktarget='' link_hover='' title_attr='' alt_attr='' mobile_display='' id='' custom_class='' aria_label='' av_uid='av-2i3x1ml']

[av_heading heading='Column2' tag='h2' link='manually,http://' link_target='' style='blockquote modern-quote modern-centered' size='' subheading_active='' subheading_size='15' margin='' padding='10' color='' custom_font='' custom_class='' id='' admin_preview_bg='' av-desktop-hide='' av-medium-hide='' av-small-hide='' av-mini-hide='' av-medium-font-size-title='' av-small-font-size-title='' av-mini-font-size-title='' av-medium-font-size='' av-small-font-size='' av-mini-font-size='' av_uid='av-15b35rx'][/av_heading]

[av_textblock size='' font_color='' color='' av-medium-font-size='' av-small-font-size='' av-mini-font-size='' id='' custom_class='' av_uid='av-k3unomjx' admin_preview_bg='']
<strong>Ist wert, daß es zugrunde geht;
Drum besser wär’s, daß nichts entstünde.
</strong>
[/av_textblock]

[/av_one_third][av_one_third min_height='' vertical_alignment='av-align-top' space='' row_boxshadow_color='' row_boxshadow_width='10' margin='0px' margin_sync='true' mobile_breaking='' border='' border_color='' radius='0px' radius_sync='true' padding='30px' padding_sync='true' column_boxshadow_color='' column_boxshadow_width='10' background='bg_color' background_color='rgba(238,238,34,0.3)' background_gradient_color1='' background_gradient_color2='' background_gradient_direction='vertical' src='' attachment='' attachment_size='' background_position='top left' background_repeat='no-repeat' highlight_size='1.1' animation='' link='' linktarget='' link_hover='' title_attr='' alt_attr='' mobile_display='' id='' custom_class='' aria_label='' av_uid='av-21n5vr1']

[av_heading heading='Column3' tag='h2' link='manually,http://' link_target='' style='blockquote modern-quote modern-centered' size='' subheading_active='' subheading_size='15' margin='' padding='10' color='' custom_font='' custom_class='' id='' admin_preview_bg='' av-desktop-hide='' av-medium-hide='' av-small-hide='' av-mini-hide='' av-medium-font-size-title='' av-small-font-size-title='' av-mini-font-size-title='' av-medium-font-size='' av-small-font-size='' av-mini-font-size='' av_uid='av-r67z19'][/av_heading]

[av_textblock size='' av-medium-font-size='' av-small-font-size='' av-mini-font-size='' font_color='' color='' id='' custom_class='' av_uid='av-k3unomjx' admin_preview_bg='']
<strong>So ist denn alles, was ihr Sünde,
Zerstörung, kurz, das Böse nennt,
Mein eigentliches Element.
</strong>

<strong>So ist denn alles, was ihr Sünde,
Zerstörung, kurz, das Böse nennt,
Mein eigentliches Element.</strong>
[/av_textblock]

[av_button label='Click me' icon_select='yes' icon='ue800' font='entypo-fontello' size='small' position='center' label_display='' title_attr='' color='theme-color' custom_bg='#444444' custom_font='#ffffff' link='manually,http://' link_target='' id='' custom_class='' av_uid='av-ka5b3zfy' admin_preview_bg='']

[/av_one_third]
[/av_section]

[av_section min_height='' min_height_pc='25' min_height_px='500px' padding='default' margin='' custom_margin='0px' color='main_color' background='bg_color' custom_bg='' background_gradient_color1='' background_gradient_color2='' background_gradient_direction='vertical' src='' attach='scroll' position='top left' repeat='no-repeat' video='' video_ratio='16:9' video_mobile_disabled='' overlay_enable='' overlay_opacity='0.5' overlay_color='' overlay_pattern='' overlay_custom_pattern='' shadow='no-border-styling' bottom_border='no-border-styling' bottom_border_diagonal_color='#333333' bottom_border_diagonal_direction='scroll' bottom_border_style='scroll' scroll_down='' custom_arrow_bg='' av-desktop-hide='' av-medium-hide='' av-small-hide='' av-mini-hide='' id='' custom_class='' aria_label='' av_element_hidden_in_editor='0' av_uid='av-2jwmt9j']

[av_one_full first min_height='' vertical_alignment='' space='' row_boxshadow='' row_boxshadow_color='' row_boxshadow_width='10' custom_margin='' margin='0px' mobile_breaking='' border='' border_color='' radius='0px' padding='0px' column_boxshadow='' column_boxshadow_color='' column_boxshadow_width='10' background='bg_color' background_color='' background_gradient_color1='' background_gradient_color2='' background_gradient_direction='vertical' src='' background_position='top left' background_repeat='no-repeat' highlight='' highlight_size='' animation='' link='' linktarget='' link_hover='' title_attr='' alt_attr='' mobile_display='' id='' custom_class='' aria_label='' av_uid='av-1fft953']

[av_codeblock wrapper_element='' wrapper_element_attributes='' codeblock_type='snippet' alb_description='' id='' custom_class='line-numbers language-css' av_uid='av-ka8ikqjt']
.custom-css .entry-content-wrapper:before,
.custom-css .entry-content-wrapper::after{
  display: none;
}

.custom-css .entry-content-wrapper {
  display: flex;
  flex-flow: row wrap;
  justify-content:  space-evenly;
  align-items: stretch
}

.custom-css .entry-content-wrapper .flex_column {
  flex: 0 1 30%;
  margin:0;
  padding: 0;
  margin-bottom: 3%;
  width: unset !important
}

@media only screen and (min-width: 990px) {
  .custom-css .entry-content-wrapper .flex_column {
    flex: 0 1 30%;
  }
}

@media only screen and (min-width: 600px) and (max-width: 989px) {
  .custom-css .entry-content-wrapper .flex_column {
    flex: 0 1 47%;
  }
}

@media only screen and (max-width: 599px) {
  .custom-css .entry-content-wrapper .flex_column {
    flex: 0 1 100%;
  }
}
[/av_codeblock]

[av_hr class='short' icon_select='yes' icon='ue808' font='entypo-fontello' position='center' shadow='no-shadow' height='50' custom_border='av-border-thin' custom_width='50px' custom_margin_top='30px' custom_margin_bottom='30px' custom_border_color='' custom_icon_color='' id='' custom_class='' av_uid='av-kbhzyilt' admin_preview_bg='']

[av_codeblock wrapper_element='' wrapper_element_attributes='' codeblock_type='snippet' alb_description='' id='' custom_class='line-numbers language-css' av_uid='av-ka8ikqjt']
// if you like the 3rd column to be expanded on bottom then change the one media query to:

@media only screen and (min-width: 600px) and (max-width: 989px) {
  .custom-css .entry-content-wrapper .flex_column {
    flex: 0 1 47%;
  }
  .custom-css .entry-content-wrapper .flex_column:nth-of-type(3) {
    flex: 0 1 96%;
    text-align: center
  }
}
[/av_codeblock]

[/av_one_full][/av_section]

if you insert this in the debug field the whole page will be there after saving.