How to catch event of Extension UI in macOS

I have an URGENT assignment with detail as below: I have an application and it has an Extension UI for it. When I select an item of popup list on standard UI of application. How can I catch event of this selection in standard UI and do update for Extension UI? Do we have any relationship between Standard UI and Extension UI in MacOS? Please help to share your experience about this technical?

How to catch event of Extension UI in macOS
 
 
Q