One way is to:
1) disconnect the fuse for the power locks
2) press the power lock/unlock switch on the door panel, or keyless entry system as usual to operate the lock
3) the clicking sound is the power lock relay, which you can use to help locate it, although if it's under the dash, may still be difficult to find.
4) if there's no sound, then the relay is toast, and consulting a technical manual specific to your vehicle, or calling the dealer, is probably the only way