From the manual:
REAR WINDOW FEATURES — HARD TOP ONLY
Rear Window Wiper/Washer — If Equipped
A rotary ring switch on the control lever (located on the right side of the steering column), controls operation of the rear wiper/washer function. Rotating the center of the switch up to the “On” position will activate the wiper. Rotating the switch ring beyond the “On” or “Off” position will activate the rear washer. The wash pump will continue to operate as long as the lever or ring is engaged. Upon release, the wipers will cycle three times before returning to the set position.
If yours won't work, check to see that it was connected when the hardtop was installed. The connector is at the rear corner, driver's side, just inside the hardtop.