I have seen videos on youtube, but none of them go into detail on how to knock someone out via pressure points.
I've done extensive study of pressure point theory, kyusho-jitsu / dim-mak, acupuncture, and traditional Chinese medicine (TCM). And for the record, I think most of it is bogus and a waste of time. There are some things about it that actually work reliably, but for completely different reasons than TCM theory suggests.
The pressure point knock-out (KO) phenomenon is caused by one of two mechanisms: 1) Central Nervous System (CNS) shutdown points, and 2) auto-suggestion (hypnosis / belief).
First, the CNS shutdown KO's are basically limited to just a few places on the body. I'll use acupuncture terminology, because that's the most precise way of targeting points on the body.
The locations that actually result in a KO are: Stomach 9, Gall Bladder 4, Gall Bladder 20, and Stomach 6.
Stomach 9 is located on the neck, adjacent to the Adam's Apple. Strikes there cause knock-outs by way of the Vagus nerve. The Vagus nerve actually measures the blood pressure of the arteries of the neck. A strike to the Vagus nerve at that location will cause a false measurement of extremely high blood pressure. The brain will receive the high blood pressure signal and will attempt to lower the body's blood pressure. Since blood pressure is actually not high for real, lowering the blood pressure will result in the person fainting. They pass out.
This can be seen in various online videos on Youtube. Here's a memorable one:
Incidentally, you don't need to strike at Stomach 9 to get a knock-out. You can get it by choking someone using a blood choke like Rear Naked Choke. A quick inward thrust on the arteries can cause it. This is why many people pass out instantly upon applying the choke.
Use major caution here, though. The arteries of the neck can tear and rupture. When that happens, blood clots can form, and that can send clots to the brain. That can cause a stroke to happen. And the stroke will happen up to days later.
The arteries of the neck contain plaque as well, especially with people over the age of 30. So attacking the neck with strikes or chokes can sometimes dislodge this plaque. The plaque can break off and travel in the blood stream up to the brain and cause a stroke.
In addition to the stroke caveat, you also have to watch out for collapsing the trachea. If your strike or choke is off by one or two inches, it can hit the windpipe, and your partner could be headed to the emergency room.
So yes, I know there's temptation to try this on your buddies. Don't. You don't want to kill them and go to jail. So just don't mess around with it.
Gall Bladder 4, Gall Bladder 20, and Stomach 6 all work in a similar way. These work by stunning the brain. You should be familiar already with Stomach 6. It's just the jaw. Boxers call it "the button". Strikes there knock people out. Gall Bladder 4 is the temple. And Gall Bladder 20 is located on the base of the skull about 2 inches adjacent to the spine on the back of the neck, in the hollow places there. These are all weak areas on the body that can shock the nervous system into scramming.
Technically, the entire head is basically one big CNS shutdown point. Hitting anywhere on the head can jolt the brain and cause a knock-out. But those 3 points I mentioned above are typically the sweet spots that require the least effort, and it's mostly due to the mechanics of the way the head moves when you hit those points. Nothing too special or mysterious.
By the way, CNS knock-outs aren't easy to do in real life. That's because people naturally flinch when they see hands coming towards their heads. They tuck their chins. They raise their hands up to deflect the blows, also. And even if you do land the strike correctly, each person has some ability to take the hit without knocking out. It's hard to know ahead of time if it will work, so you have to have a back-up plan and be able to fight. There is no way around it. Learning tricks like this is no substitute for training how to actually fight.
That's about it. The other places on the body that are pressure points aren't going to reliably knock anyone out. This is despite what kyusho-jitsu people believe.
Kyusho-jitsu theory uses the Five Element Theory, the Mother Son Law, Meridian Theory, and other theories from TCM. It uses acupuncture, in other words. Only, instead of trying to heal people, they try to do the opposite.
One of the ways Kyusho-Jitsu is supposed to work is by combining points in the "destructive cycle" of 5 Element Theory. So you hit a point on the arm, a point on the torso, and a point on the leg, and the combination of points causes illness, knock-outs, or death.
That's how it's supposed to work in theory. In actuality, Kyusho-jitsu / dim-mak doesn't really work. The practitioners that demonstrate it working all do so on their own students. In other words, it works on "believers", but not on skeptics or people who have never seen it before. This fact has been proven many times.
In order to make it work on non-believers, kyusho-jitsu people rely on one of the 4 central nervous system shutdown points that I already explained. If you hit 3 different points, and the last one you hit is one of those 4 CNS shutdown points, they will get knocked out. But they'd accomplish the same thing if they merely skipped the first two points and went right for the last point.
There are a lot of other weak points on the body that, when hit, cause pain or cause people to lose structural stability, but not knock-outs. Places like the solar plexus, the testicles, the eyes, the nose, the ears, the arm pits, the floating ribs, the liver, the kidneys, the back of the knee, etc.
There are some reports of people being killed after being struck in the solar plexus. Apparently there's a nervous system connection between the solar plexus and the heart. But it's a pretty unreliable connection. You have to hit it at just the right moment and with enough force. It's not something that really ever happens in professional fighting (boxing / MMA), so it's not reliable.
In summary, most of what you hear about pressure points, dim-mak, and kyusho-jitsu is pretty much bogus, with the exception of CNS shutdown points. Do yourself a favor and don't waste any of your time on it like I did.
Hope that helps!