I raise 4BB's under the gun and villain is on the button. Effective stack size is 100BB's. Stakes are $0.02/$0.05.
What is the chance of someone flopping trips by the way, is it higher with 2 opponents? If the stakes were higher, say $0.05/$0.10 would this make a difference as the stakes increase? Do stack sizes matter? Also what if it was the other way around and I had position on villain instead?
6 or 9 handed?
I don't play much 9 handed so I won't have too much insight on that. 6 handed, while you gave examples of paired boards, they play entirely different in my opinion if I'm holding Aces.
K55 - If you are facing a raise behind you after betting on the flop, you're good almost 100% of the time here. The only
hands beating you here are exactly KK, K5, 55. You can eliminate K5 right away because villain is almost NEVER calling with a raise behind. KK is likely to 3bet in most situations, and 55 is SO unlikely. Now, if you run into them, tip your cap, say gg and play the next hand.
But back to my first sentence, if you're facing a raise, you want to start to think of possible ranges that your opponent has here. They're probably holding strong Kx hands (AK, KQ, KJ, maybe KT). You want to keep their bluffs in as well, so calling is likely the best play here, but if you have some history against the villain here, and they're likely to go crazy with Kx hands, then raising is perfectly fine here. The key is trying to extract maximum value here. So your betting on the flop here is good.
JJ2 - I'll comment below.
Then I wouldn't see the K55 as much of a threat. They could have called with a good Ace or two face cards, or a low pair. The JJ2 would seem like more of a threat, but I would do a continuation bet on the flop, roughly half the pot.
I agree with Mortis here. You should be betting most boards, even paired ones. You can't be afraid to play your hand fast. Also, your opponent may be thinking that you're full of it, that they're not putting you on Jx here. They could very well have QQ or KK, which is entirely possible, though they may be 3 betting you pre-flop with KK some of the time. Sure, it is certainly possible that you ran into trip Jacks here. So going back to the line you took, if you bet on the flop, then villain raises, you can 3bet. They will probably fold enough of the time that it makes this play profitable, though I'm curious to what others on here think.