Further to a previous question asked by someone else, Is it actually possible to knock someone unconscious by giving them a sharp blow to the top of the back ? (just below the neck) like you see on many films (especially Bond films)
There are pressure points (dimmaks) around the body, which are usually where meridians cross over and when pressure is put on these points, the blood supply can be weakened. You should never abuse this sort of knowledge, and if you use your energy properly, you will never find yourself in this situation!
There is no secret trick to knocking someone out. Striking pressure points on the back of the head or in the front or sides of the neck and throat do really work. But they dont work any better than a right cross to the forehead! Striking pressure points obstructs the blood flow and essentially causes a "black out" from lack of blood flow. If you strike someone (preferably unaware so they cant tighten muscles or prepare for the blow) in the head, the head rocks , the brain sloshes around inside the scull, and as the head and brain move uncoordinated with eachother, it pinches the nerves and blood supply and basicaly results in teh same thing. The infamous karate chop to the base of the neck is just a hollywood glorified way of doing it.