There are few ways in which you can identify the program for editing if you know the transaction code in advance.
Firstly you can useSE93 for identifying the program on basis of the transaction.
Secondly, you can run the TCode, and then drill down to program from menu. You can lead to program from System → Status → SAP Data → Repository Data →Program.
Lastly, when you run the T-Code, in the SAP GUI you can see an arrow in the bottom of the editor, Just click on it to get more information about the transaction. You can get details including the program using these.
A small note, the first option should work universally but there can be some scenarios where the last two option not work as expected. So go for first if it is fine for you.