which pick up does the treble and the rhythm switch use on my les paul electric guitar.

The treble pickup's at the bridge, the rhythm pickup's at the neck.

Really, you couldn't use google?
i think you can hear it by switching to either one which you think it is, then tap on it with your pick. it should be louder on one pickup than the other so you know which is on
Main gear
  • ESP Eclipse II Standard (BK Cold Sweat)
  • ESP Horizon NT-II Standard (SD '59/JB)
  • Marshall JVM 410 Combo