Thought I'd just add something to this thread.
Firstly, well done to Khoveraki for spending a good bit of time reading up on everything and posting. Though I feel some of what you've written can be clarified a wee bit.
The three nerves you have given as an example are not in the jawbone (mandible) but are Cranial Nerves which branch out from the Medulla and though they have distributions around the mandible, none are actually located within it. The only nerve located within the body of the jawbone is the Inferior Dental Nerve - which is a branch of another Cranial Nerve - the Trigeminal.
However, as these nerves exit from the Medulla, they are linked to the brainstem - and it is injuries to this area which can result in a knockout. Not being hit directly on any of these nerves.
The actual intricacies of a knockout (such as how the brain shuts down and consciousness is lost when it happens) are still relatively unknown, though hitting a 'nerve' in the jaw will most definitely not cause any form of unconsciousness. This arises from trauma to brain cells or the brainstem. The reason that getting hit in the jaw results in more knockouts than hits elsewhere is because it is a loose projection attached to the bottom of the head and a hit here results in the mandible accelerating quickly, and thus a sharp rotation to the head, causing direct or indirect trauma to the brainstem or a sudden jolt to the brain, which can accelerates so fast it hits the skull before the cerebrospinal fluid which protects it can act as a shock absorber - thus resulting in brain trauma, and loss of or a decrease in consciousness/awareness.
You can increase bone density in the mandible through bone hardening (cortical remodelling), though you have correctly pointed out that no amount of trauma to this area through punching oneself will help stop a knockout. What would help stop a knockout however would (as pointed out by Slapshot) be to keep your chin tucked, as well as having the jaw closed tightly. Strong neck, masseter and temporalis muscles would aid this (along with a good mouthguard and being fit enough not to gas and leave your mouth hanging open during a fight!), and this would help ensure any blows to the jaw would ensure the head is not rotated too quickly, and the tension in these muscles being released on point of impact, would help absorb some of the blow from the strike.
Hope this helps.