89o, flop

I don't like the donkbet. It shows that you have something, it mostly reps 9x, your exact hand. So he can play perfectly against you. BU is often folding anyway on this dry board. If it gets heads-up I would c/cdown on good cards hoping to induce bluffs or thin valuebets with 44-88.

edit: As played you have to call down as well as he might think you're on a bluff and try to rebluff you. Thinking about it, against aggro fishy villains the donk can't be that bad to induce a bluffraise, but c/r might be even better

I don't like betting either. No matter which hand you have: Check! By checking you have a 100% Range and by betting you devide your range in a range that most likely has hit something like here with 9x and the other part is more likely to be nothing then. You wanna have a 100% range with hands like 9x Ax and even nothing when you check. You wanna keep your range balanced and not wanna play obvious like

bet = i got something

check = i have nothing

And you can't bet for value. You may scare him off of hands like KJ where he does still have 6 outs against you but against his entire range, including too many Ax and Overpairs like JJ etc, you are behind and after this raise you can't well define your opponents range since he may put you on a bluff, he is unknown, he may rebluff you and you are quite committed to call down for an unnecessary more investment. Just check and see what happens. If BU folds you can 3 times check/call on blanks.

with a read that CO would "never" bluff you can immidiately fold the Flop. It's kind of exploitive but there are too many nits out there who never raise with something worse than your hand.