If you have a meter you can check that you are getting voltage to it. Either check voltage at the contact points on the boot floor, the two on the right, one is a permanenet 12V to the motor, the one on the left is a switched 12V from the wiper stalk, when you turn the stalk you should get 12V here, check to nearest earth. The earth from the motor goes down the other lot of contact points on the left but don;t worry about this.
If you;re not getting voltage here then check fuse.
If you are then I would carry on as follows, remove plastic trim from inner tailgate, remove parcel shelf, remove rear wiper arm, shut the boot. Get in the back seat and unbolt the wiper motor, turn it around, at the end you should see two wires which are going to the motor itself, brown & green. Check that you have 12V across here, if you don;t but you are getting 12V at the connector then the relay is not working on the motor, if you are then the motor is nackered.
HTH.