UTG is a good player
CO is loose/passive (but he does bet and raise with strong hands)

5/10 (5 handed)

Preflop: I get delt K ,T on the Button.
UTG calls, CO calls, I call, SB folds, BB checks.

Flop: (4.5sb) A ,T ,6 (4 players)
BB checks, UTG checks, CO bets, I raise, BB folds, UTG folds, CO calls.

Turn: (4.25BB) Q (2 players)
CO checks...

who checks and who bets?

I fold the flop.

What's the point of betting?

The hands that you're going to knock out are ones that you have beat pretty badly.

There are few legitimate hands that he could reasonably be holding that dont have you beat. 10/J, 10/9 and a pocket pair below 10 are the hands that will fold. A weak ace and a queen will call. A straight, two pair and a strong ace will raise.

The raise bought you a free turn, so take it.

Cool. I took the free card and the river was a brick. He checks, do I value bet?

i think he has AQ, or nothing.

Maybe QJ...what limit is this?

I wouldn't. He could still have a weak A or Q, (nm on KK/JJ, he limped preflop) and he will probably call you with all of those. The only hands you beat that he calls is probably JT, T9 or a lower pp.