Where would it be?

I looked for it and according to the RPO codes it has one. If it's not there, what kind of wiring is it, so I can put a new one in

 

Probably just an error in assembly, was supposed to be installed but was missed. You should be able to easily find it as they are very evident, usually mounted near the tunk latch facing downward of course. Most of those are mercury switch controlled and you can actually use one from almost any GM as the all work the same. One wire to contstant 12 volts and then the ground is supplied by the mounting screw, when the trunk is opened the mercury switch makes a circuit and the light illuminates.