This all depends on villains 3bet tendencies and where he is 3betting you from. If I open UTG 9-handed with AJo and get 3bet by villain UTG+1, normally I would just fold. This is not a question where you will have one answer fits all unfortunately.
However, if you want to think of it in terms of GTO, think about how many hands you are opening in the particular position you're opening from and whether it's at the top or bottom of your opening range. For example, if you're opening ATs+, 77s+, KQo, AJo+, or something like that, AJo would be near the bottom of your opening range and it becomes a fold facing aggression OOP against a standard player. Also think about how WELL your hand plays against 3bets. Small pocket pairs, suited connectors and suited broadways play better than weak Ax offsuit type hands because they can flop more equity and more draws that make your hand easier to play. You can't account for every single variable possible when facing a 3bet, there are a lot of factors that go into whether you should fold, flat or 4bet for value or as a bluff. This all depends on villain, stack sizes and relative position. Hope this helps!
~TCashMoney19