Did you know you were dealing with a donkey? In a vacuum you played it fine. If you're getting action when you go raise/pot/pot with AA then two-barreling in a spot like this is the price of doing business.

Firing that particular river card would be pretty silly. However given your line I don't see how you can ever bet the river. Your opponent has check/called two big bets and it's going to be really expensive for you to make him consider folding, which he won't do often enough anyways given the action. But if you knew that this opponent is bound to hang in to the end with draws and 3rd pairs, when would you rather put him to a big decision - earlier in the hand or later?

2nd barrel is fine here...he's just either REALLY intent on defending, or a total donk. I think at first he was defending, then he picked up the FD and thought he should call pot

Bet this turn every time.

Think of it this way: You have JTo and call in the BB, see this flop and the raiser bets. It's a CB and you beat a lot of hands. That's it. Then a King comes and when the aggressor makes a bet like this, you have to re-evaluate what you beat and how you fare against that range. If the turn's a deuce, you're not so much re-evaluating as asking how capable is this person of double-barrelling big cards to a blank board?

You force him to have AT or an Ace high FD here and that's good. What's better with this turn card is that if he floated Ace high on the flop, it's tough for him to check-raise.