I think fold AK is pretty easy post flop but can be hard preflop. If there is more than one person all in pre flop, I may fold depending on opponents history, their stack//vs my stack, my position in the tourney, how close I am to cashing etc. It's a risk vs. reward decision for sure. Post flop, it's pretty easy to know when you're beat or ahead with AK. If the flop comes out dry, you throw out a c-bet out of position, opponent will either fold, call or raise. Folding, well it's obvious, calling can be suspicious if there is paint on the board or a draw of some sort, and raising, well, they have it. A lot of times if a draw misses, I'll throw out another bet on the turn and I'll usually get a fold. If someone jams and I have top pair, that'll be a hard one but they might just have a lower pair but could have hit trips. I'll only call in that situation if I can afford it.
KK is difficult pre, but not so much if one or more people are in the pot and bet with an ace on the board. A c bet in position after a check or if they bet on the flop usually indicates that they hit their ace... usually. I think it's close to 25% of the time that an ace hits, someone has it