How good is an underboat in this game?

The preflop call was iffy, but very low -EV. Odds will make a set with a pair in the hole on the flop is 12.43% or 1 in 7.04. When you called there were only 3.5 SB's in the pot, not enough to call, but you lucked out and got 2.5 more bets after your call. That means you were just over one bet shy of what you needed. So still -EV, but not that much. Nevertheless those fractions add up over time, so watch this leak. In O8, 99 can only be played for set value. Take advantage of position, here you don't have it so I would recommend a fold.

Your flop raise was good. You have to test your hand, and you will make a fullhouse 35% of the time if you take it to the river, so you can take on the flush draws. There were no re-reaises, so like below, I feel you have the best hand. KKxx has to raise to fend off the flush draw and build the pot for his own good. The odds you do not have the best hand here are slim slim slim. (If you don't the other person is not paying attention, or even better, is an idiot.)

Turn - you have to bet here. The most likely draw and only smart draw is a flush. It didn't hit, but someone could have made a str8 or str8 draw. Make them pay if there are drawing, and if they have it, they will probably announce it with a raise. Not raising cost you information. (Edit - what I mean is you raise, a made str8 has incentive to re-raise b/c maybe he may be able to chase out the flush draws facing 2 BB's. (Doubt it, though, this table seems quite loose, which by the way is why your call was probably only slightly -EV in spite of only having 3.5 bets in the pot.) You have 10 outs, so of course you are going to call the raise, but if the board doesn't pair you will have a good idea about the strength of your hand.)

River - underfulls are scary in O8, but they stand up very regularly. Without crazy betting, see the showdown, especially when the pot's big and no one else has represented trips on the flop. Occasionally, someone makes a fullhouse here b/c they had two pair on the 1st Jack. So what, with the pot so big, not calling is always a bigger mistake than folding. With 23 BB in the pot, and one bet to call, you can lose with your underfull 22 times and still break even. You will win with an underfull way more often than that. Folding here would be HUGE a mistake.

So other than an iffy -EV pre-flop call this hand was well played, IMHO.

2nd Edit - for some reason I misread the turn betting, there was some raising after all, there is your str8, like some one said below.