The first point to have a look at is the check valve. If you open the boot and undo the headlining along the back of car and pull it down a bit, you can see the pipe going to the nozzle. About 3" back from the nozzle is one of those little check valves, like the ones just below the nozzles under the bonnet.
On my old 9K, this was the problem. Even if it isn't, when you unplug the pipe here you can see if the fluid is getting that far at least. If it is, and the check valve is OK, then it must be the actual nozzle, which you can usually clean with a needle - or compressed air.
Hope that helps!