Failed to trap with AK.

That's what you get for playing it like this !
Always 3bet SB vs CO.
As played bet/fold OTR, he has it. Be it 88, J9, K8, 78 or T8 or I don't know what, but he should have it.

It was already opened by 3bet, so when you say always 3bet, you mean to instead of calling at preflop, reraise the CO with another 3Bet?

P.S: You mean you never try to set the trap like that?

3bet is third bet. Big Blind is mandatory 1st bet, CO’s raise is 2nd bet, your raise would be 3rd bet or 3bet, if someone reraise you it’s 4th bet or 4bet... hope you understand now how naming convension works.
About the hand... You really should 3bet with AK. If you called then just bet, bet, bet, and fold vs raise. It’s tooooo weak hand for any kind of traping.

When someone opens for example 3bb does not equal to a 3-bet. A 3-bet would be if you reraise that open.
So Villian bets 3bb and you 3-bet him to let's say 12bb (3x the open).

Yes that was a confusion for me. Now it is cleared thanks. ♦

I actually don't think that we are trapping here, do we?

Hmmm. As a new learner, in my noobish vocabulary:

I go in with AK, hit a K at flop. As flop is rainbow and I have the top pair top kicker, I told myself "this guy had raised before the flop, so right now if I check, he will continue betting and betting. I have top pair, board is not dangerous, so why worry? even if an Ace hit the turn, I will hit two pair"

Honestly speaking, I thought it was going well to let him finish all the chips on betting. It is not kind of a trap? Then in what case it would be a trap?

P.S: I have a mindset of involving so many ppl in a pot when I have a good hand, then following that method I said (so called trap), I let them bet, then I bully them out by reraise. Apparently this mindset is not a good one and I have to change that.

BTW because you just called preflop he can have all the hands MyFloxyBaby mentioned, and that’s why your hand is actually too weak for trapping. If you have 3betted him (re-raised) preflop he would have to fold all those hands and than your hand is much stronger but it’s still not too strong. He still can have 77 or TT, and you’re almost dead against it, or he can have hands like AQ, QJ, and trapping against those hands is like calling for disaster. All in all, don’t try to trap with anything less then full house. That’s just my experience.

Traping is for when you have more or less locked the board (and thus are not afraid of giving a free card) and can't value much of villain's range, for example AA on A72 rainbow is ok. He can't have much, and when he has 77 he is gonna raise/reraise later by himself so you don't miss much value (unless against stuff like AJ maybe but few combos here).

One of the reason traping isn't great in most spots by contrast with this example is that people just don't raise/reraise medium strenght hands on a later street just because you have checked once before. Their range becomes much stronger so you are gonna impale yourself against good hands is all or nearly. And you're just gonna stupidly lose a street of value against a lot of so-so hands. Say if you had AK on the same A72r board you want to just bet-bet-bet and get called by lower Ax. Against those a street checked is just a street lost. Getting fancy will lead you nowhere.

Generally speaking one pair hands are somewhat (but not that much, careful) strong but vulnerable hands that need to be betted to deny equity in villain's range. The more you'll progress at this game the more you'll understand how much denying equity is paramount in it. In villain's range there are a lot of hands, and most of them have a significant equity, even if they are behind, so allowing him to realize it freely is a gift you are giving him.
(Not to mention it's harder to bluff if you don't bet when you have it. It's best to bet with a mix of value and bluff and thus earn a lot of pots than giving up too often.)

The two main reasons for betting according to Matthew Janda are making the pot bigger in case we win and denying equity to villain's range (that's why you always want to 3bet AK SB vs CO, to deny equity to his wide opening range). Each time you contemplate betting or raising you should ask yourself if you are gonna accomplish those things well or not. Is your equity robust or not ? For example you don't want to raise A3 on A72r because you're gonna get called mostly by better aces so you turn a good calling hand into an awful raising hand so much your equity drops by that change of line. On the opposite raising a flush draw can be good because when you hit your flush you are still mostly ahead of villain's shove calling range.

Too many comments with too much text

Again re-buy to 100bb.
3bet (re-raise) pre-flop.
As played, you are behind OTR. The river raises are almost never bluffs.

You don't trap at NL2. There's no need for it (there are always spots for that, but are not that much: specially very dry boards with monsters hands and that's it).
Just 3bet / bet /bet. Overfolding to rivers raises with no info and with TP hands is totally fine at the micros. You won't be exploited by doing so.