Was driving my 03 wrx today and something went clonk, and now when I drive it, it makes a kind of knock knock sound when I change gear or go around the corner, or wiggle the steering from left to right so that the car shakes about I can hear a knock sound, and there is no drive to the rear wheels, have I popped the propshaft out maybe?

 

Propshaft is bolted in place, so Nope you most likely haven't popped that out.

You could have popped out a rear axle though, they are bolted on the wheel side (by the 32mm nut through the bearing/hub) but are just held into the diff by a spring.