First thing is to get a repair book that has a good circuit diagram in it. There usually is a wire that runs along the driver side pillar area from the wiper motor connection to the interior fuse box. Sometimes it goes under the carpet retainers in the door area or it comes down the driver windshield pillar.
I don't have much knowledge of the Tahoe design but most Chevy's incorporate the rear window washer with the front washer motor. So if the front is working, and this is the only motor, then there is something wrong in the delivery line to the rear. If, the Tahoe, has a separate motor for the rear then you have lost voltage to the entire unit. If this is true then the first place to look for voltage is loss is at the motor end. Find the wires that connect to the wiper and (if correct) the washer motor in the rear door area. Put a voltage tester on the + and - wires that go to those motors. Don't ground to the chassis when doing this. Usually, these motors are protected ground and won't ground to the chassis at the point where they are attached to the vehicle. If you get voltage at this point then the motor has a problem. If you don't, then the wiring has a problem. Check fuses first. Then use the diagram for the wiring and find the bad spot in the wires.
You will need someone to help you do the testing, since you have to turn the switch on to test the wiring.