Referring to this column
FWIW, a knockout shot to the head is the most difficult way to do it, and it’s the most dangerous to the recipient. As Cecil mentioned, that causes injury to the brain itself, and if that injury is severe enough, it can potentially kill someone.
A much easier way to put somebody out is a shot to the brachial plexus origin pressure point. The BP origin is on the side of the neck; think of hitting Frankenstein’s creature (the Boris Karloff version) on one of his bolts. A moderate blow, similar to a backhand slap, will stun someone. A hard blow, such as slamming the forearm into the side of the neck, will actually cause them to black out.
This is a primary pressure point techique, taught to police officers and in martial arts schools worldwide. The effect will not last long; even a hard shot will only black someone out for about 10 seconds. However, that’s long enough for you to either get the cuffs on him or run like hell, depending on your objective.