How to find menu-item identifier for functions.php purposes?

I’d like to re-use an old topic but I don’t know how I can identify a menu identifier. See:
old topic

Mike refers to menu-item-2339. How do I find the menu item nr, so I can use this approach for future sites without having to open a ticket?

• This topic was modified 1 hour, 58 minutes ago by the_digital_manager.