3 betting pre-flop is an option especially since you are on the button and you probably should be 3 betting from the button to steal some of the time anyway so I feel a 3 bet here balances for when you have air / are on a total steal. I know its a UTG raise so you may not want to 3 bet quite as much as UTG does still need to be given credit unless you guys have history and or you have noticed that he raises pf utg often. IMO flat calling pf is probably not the best way to play this hand as there are probably going to be overs on the flop which will make your deicisions on the flop, turn and river more difficult, also you could win the pot with a 3 bet pf as he could fold (we know he has KK so hes obv not folding but raising always gives you another way to win the hand) and you don’t have the proper stacks to set mine here.

If you 3 bet to say, 21500 and he ships then you have a tough decision to make (it could be AK,1010,QQ,KK,AA etc). I would think most pros probably lean towards a fold if he ships as you still have over 30 bigs if you fold. A10 probably chk-raises as well as 1010 and any over pairs just as he did. Under pairs probably choose a check-call type of line to get to showdown cheaply esp since he is OOP.

Not sure how to play the flop in this situation if you were to flat call – Would flatting his c bet and then re-evaluating on the turn be the ‘safer’ line here? I guess you don’t want to see an Q, K or A on the turn so probably raising on the flop was the correct decision but once he shoves you really have to try and figure out what you are beating. Tough spot post flop if you just decided to flat call his c bet.