Some front ends will show a labeled cp, with your mapped buttons. I think GameEx is one.
It's not too hard to figure the buttons out or even to reconfigure them.
For example, for a game like Donkey Kong, you can configure both joystick for up, down, right and left and let the player grab either. I even map 3 or 4 buttons to 'jump' so that a player will find one that works.
I know, its easy for one button game, but you might be surprised how easy it is to figure out the buttons for multiple button games. Play them once and assign what feels right (or what is accurate).