I use EightyOne. Open Tools > Debugger window.
When You press the stop button your code is shown. It's tricky because the video routine takes most of the processing time so you rarely - if ever - land in the game code.
To get to the game code you must set an Address type breakpoint using the 'greater than' evaluation. Break when address > $4000 and you will hit the game code. This type of breakpoint will trigger on every instruction so you need to delete it once you've hit the game code.