I am assuming that your front washers are working OK.
First thing does the washer motor sound as if its under load (pumping water) or just free wheeling at high speed? If its running fast the impeller my have come off the motor spindle.
The washer motor pump operates both front and rear washers and a valve on the bottom of it switches which either front or rear depending which you select just by changing the direction the motor spins.
Otherwise take the rear wiper spindle cover off, then pull the spray head part out, its held in with an O ring.
Try the washer again with the nozzle out and see if there's water coming out.
If not, the water feed goes straight through the wiper spindle from the inside, so If there's no water leaking out of the boot maybe it is collapsed as it comes through the hinge.
Unclip the off side boot hinge cover and check.
Lastly the washer pump itself, jack the off side front up and remove the wheel. Remove the wheel arch liner (dont break the clips!) to access the bottom of the washer bottle.
Pull the washer pipe to the rear washer off the pump and try again. No water, faulty pump. Part number 1K6955651 I think.
If the pumps working to the rear, start looking for soggy carpet inside down the drivers side from front to back!
Best of luck and wishing you a sunny day to do it on
I hope this helps