help with MUX shield Needed

hi guys, as still new to hear, i was hoping someone could help me find out how i locate what pin numbers are being used from a MUX shield.

its from the - YAAMI drum kit with piezos.

here the code is located.

i am trying to find out what pins to connect the pizos to so if anyone can help then please message away. like i said i am still very new to arduino.