As ABAP Developer debugging process is a vital requirement during create ABAP Program, But i think doing debug in SAP ABAP is the most convenient because SAP own user friendly ABAP Debugger.
There are numerous way to debug ABAP Program is one of them you can write BREAK keyword on your ABAP program or put your breakpoint or watchpoint. but when you will debug popup you cannot run any /h or any do any activity until you pass popup unless you run ABAP debugger before calling popup screen.
But there is a way to debug popup, you need to open notepad and copy paste this code to it.
Then saved it as batch file ( .bat ) for example you can named it popup_Debug.bat. Now when you want to debug any popup screen you just drag popup_debug.bat file from windows explorer to popup screen.