In the Job Overview transaction SM37, select the job that has finished and enter jdbg in the command field. The Debugger will start. It will simulate the exact scenario with the same selection screen values, and the system variable SY-BATCH will be set to X (abap_true).
The new ABAP Debugger is executed in its own external mode, while the application which is being debugged (debuggee) uses a different mode. This is two tier architecture that is the new debugger is displayed in its own GUI window. The debuggee is inactive while the debugger is active and vice versa that is debugger remains available in inactive mode when the program displays its final output. The debugger does not close while the application which is being debugged is still alive.