Hi, what do you cbet on dry board? what strategy use here? how many % do you cbet on similar boards? what sizing? thanks

Poker Stars, $0.50/$1 No Limit Hold'em Cash, 6 Players
Poker Tools Powered By Holdem Manager - The Ultimate Poker Software Suite.

Hero (SB): $121.73 (121.7 bb)
BB: $100 (100 bb)
UTG: $24.62 (24.6 bb)
MP: $100 (100 bb)
CO: $105.18 (105.2 bb)
BTN: $124.75 (124.8 bb)

Preflop: Hero is SB with X-X
2 folds, CO raises to $2, BTN folds, Hero raises to $8.50, BB folds, CO calls $6.50

Flop: ($18) J 2 9 (2 players)
Hero ?

Considering that you flop a pair about 1/3 of the time with big cards, a starting point for c-bet % could be about 50%. You could spread that out as betting 2/3 of the time when you hit, and 1/2 of the time when you miss. That means 22% of the time you're betting when you have it, 33% of the time you're betting when you don't have it, and 45% of the time you're checking. You can adjust based on your overall strategy and opponent profile. Sizing can stay the same with different hands, or change with the same hands, again depending on the same things. Sizing can tyipcally be in the 1/3 to full pot range. There's no set guideline, other than the obvious exploits. If your opponent is fit or fold for example and doesn't adjust, bet 1/3 when you whiff and bet more when you hit.

What hands do you 3bet with pre?

And what is the villain's 3bet calling range?

Once you know these, then the strategy will be straight forward based on your ranges. If you don't know the villain well, what is the 3bet calling range for an average villain at 100nl? If you are new at 100nl, what was the 3bet calling range for the average 50nl villain?

If you don't know any of that, you should be moving down much smaller stakes.

3-bet pots OOP play very differently to single-raised pots in position.

On that J92r where hero 3-bet in SB v CO, it's probably optimal to c-bet something silly like 25% of pot with almost your entire range. In a single-raised pot where you were in position vs BB, you'd pick a larger sizing and a lower frequency.