My thoughts are first and foremost improve your defence. Secondly being aware of an incoming punch or not plays a role in this, you subconsciously brace or consciously try and roll with it, or slip, or move, or block etc. As far as strengthening goes I'd imagine it can be trained to a small extent by getting your neck stronger in all angles, get your spinal erectors stronger which will take the "shock" and even maybe your lower body stronger to maintain a solid base. All of this will be 5-15% at most really, I imagine jaw strength might have something to do with it, but by and large there will be a few other factors like adrenaline, heart, body language, stance, balance that will play an equal role.
strong strong legs! will help you take a shot, strengthen them some fighters when there hit good, there legs go to jelly
A correct mindset. You have to accept that you WILL get tagged hard and that you WILL get hurt at some point during the match, session, whatever. By recognizing this, you won't be so surprised by when you get hit. I know this firsthand and the calmer and more relaxed you are, you'll maximize your effectiveness. Next step is rolling with the punches and making it so that they won't land with full power. Always keep that head moving or else the other guy will move it for you.
Improving your chin? Not really. Taking punches better? Keep your eyes open and try not to let them land.
its all mental man,when i try to box clever i can get hit by a little jab and my chin gets shattered lol but if iput the mentality in like "im having this ****ing **** now" and go after the guy i dont feel any punches at all
i do alot of neck bridges, neck ups with a plate on my forehead, neck rotations, i used to do some jaw work but i found it did more bad then good and was apparently useless from what id heard. thats only a last defense when you actually do get hit with punches. a strong neck can act as a shock absorber, but it can only help so much. you either can take a punch or you cant.
Like most people said having a strong neck will improve your chin. But having strong traps will also improve it too. I like to think of the neck as the primary shock absorber and the traps as the secondary shock absorber.