Surprisingly the amount of force it would take to knock a person out with ta blow to the temple is 400 pounds. You can also punch a person out by punching them in the chin in which there is a main nerve that will knock them out.
1 Additional Answer
The amount of force to knock someone out is about fouro hundred pounds of pressure to the temple. This is the easiest way to do it and does not need to cause a lot of head jerking. Only professional fighters should use this technique as this is very dangerous.