I believe the issue with Roach was less about his know-how and more about his emphasis. If he only had so much time with Amir, a well-rounded approach wasn't entirely feasible. One has to recognize that Khan's defense improved since hooking up with Roach in terms of his use of the jab, movement, control of distance, and high guard. It's only recently he's deteriorated and acted a fool, making his flaws more exploitable than usual.
Being able to take a shot - can be improved, like Ariza said.... first thing that goes when taking a flush shot is the legs. Think if he strengthens his legs and neck muscles, he'd be able to take a flush shot better, but Hunter could improve his defence so when he is taking shots, its semi flush instead.
Thing is though I don't think Khan's defense is all that bad to begin with, its only horribly bad when he is hurt, I hate to keep beating a dead horse but it all goes back to his chin and that he can't take a good punch without some obvious signs of being hurt.
I don't think he can learn defence as such, he isn't going to move his head or master parrying punches or get better footwork. He can probably work on varying his attack, clinching when he needs to and using his jab more. That should help him from getting timed as easily but I think once he gets hit he will revert to his normal style.
I think Khan has all the tools, speed, size, length and skills. He became predictable under Roach, and was ignoring the fundamentals. If Hunter can help him get his confidence back, start working behind that jab, maintaining distance and using his physical advantages then he can be champion again. That glass jaw will always be a weakness, but if he makes the most of what he has, he's still a world class fighter
hes always had the same problem and he referts back to it. u saw his fight with malignaggi, he was brilliant. he used distance and his jab. then, against maidana he went back to being careless, throwing punches in bunches. when he threw an uppercut i believe against garcia, he was squared and had his other hand down, the rest was history.
I think, and hope, Hunter can help improve him, but to what extent we'll not know until Khan steps in with a big puncher again. We need to know how he'll react when being hurt. His decision making, that is. Not chin.
I hope he doesnt become like that boring sob Andre Ward. If he wants to claim a big victory against Froch good for him. But if wasnt for Ward running and if he would of stood his ground and fought Froch woulda knocked him out