To trigger your Engage Box when a user click on a menu item you only need the specific menu item's class.
How to find the menu item's class
- Go to Menus All Menu Items
- Write down the ID at the far right of the menu item you're interested in like in the picture above
- The menu item's class is .item-ID where ID is the number you wrote down previously
How to configure your Engage Box
- Go to Components > Engage Box
- Create new box by clicking on the New button from the top bar
- Write your own message on the Custom Text field
- Write a title in the Title field
- Under the Trigger tab choose on Click on the Trigger Point field
- Type in the Trigger Element field the menu item's class you found previously
- Save your box!
The method shown above on how to find the menu class is possible only when the template hasn't overriden Joomla's default configuration.
In that case take a look below on how to find the menu class with Google Chrome.