Navigate to this path in a file manager: /usr/share/applications
For example, with Nautilus you would run (in a terminal)
nautilus /usr/share/applications
Locate your program by name (using search if required).
Right click the file for your program. Select 'Properties'. There should be a 'Command' field which shows the command to be executed. If the program has arguments such as %U, those are file arguments passed when that program is used to open a file.