The questions in your most recent post are really general, but its just like c-betting in any other pot. You take into account your hand, your position, his range, and fire accordingly. Its just that for 3-bet pots, their range is usually stronger, and (usually) contains less speculative hands like 78s/22/ect. So with their stronger range, you just need to adjust what you consider a wet board (a 78J board is wet for a limp/caller, but not in a 3-bet pot imo). Also, since their range is stronger, you should c-bet less often and smaller, since your c-bets will work less and you don't need to bet as large to get it in by the river.
If villain is raising 8% of hands, and folds to c-bets 90% of the time, we should pretty much never c-bet anything unless we can beat aces or kings.
So I'd look at this guy's fold to c-bet stat, and if stuff like AQ/KQ/99/77 is in his calling range, I go ahead and fire this flop. The flop isn't especially wet, we have two overs and the nut backdoor flush draw. So if his range isn't especially strong, then I think we can fire out ~$4 here given our equity and the flop texture.