The easiest and most affective way to knock someone out is easily practiced on a mook jong. (Sales pitch: Buy one from me!) What you first want to do is put your left hand on the left side of their head and push to the right. What that does is it makes the left side neck muscles relax and the right side neck muscles tense. It's exactly what we want them to do.

Now, for the strike you will use your right hand to do a suto (knife hand, judo chop, etc.) to the left side of the neck. It's the same side that your left hand is pushing against. You want the strike to be perpendicular as possible when you strike their neck. Very little force is needed to knock someone out in this manner.

Don't practice this on your little brother, spouse, or training partner because if you use enough force (which you want to do in a fight) there is a pretty good possibility that is will cause brain damage. So, the moral of this story is to Sales pitch: buy a mook jong from me!