Problematic hands

This is too vague of a question for it to be constructive. Your statement that you often 3-bet them is good.

i often 3 bet KJo, AJo as a bluff. don't want to call with them as they can be dominated. i 3 bet TT but don't know exactly why. what about calling them IP?

It will depend on your position, the position and style of the pre-flop raiser, players behind you, etc. Maybe post a hand or describe a more specific situation.

3 betting them isn't generally bad. Depending.

The 4 hands you mention are all hands that are strong starting hands (i.e. generally have good equity), but are also vulnerable to being dominated by better hands.

That means they just need to be played more cautiously.

Maybe three bet less against players who are raising tight. Against those type of tight players you want to play smaller pots. Against looser players, be more aggressive in 3 betting (and sizing). Also call looser.

Strong but vulnerable hands are the type of hands that separate the men from the boys so to speak.