most important thing to do is to look at what they are donking with when they get to showdown. They usually dont do it with everything, sometimes its only with air, sometimes its with draws, sometime with middlepair, sometimes with top pair. All fish are different and knowing which donks with what should be fairly obv of what to do from there on. e.g., if they donk with pairs, obv raise for value type hands and fold the air of your cbetting range.
most fish do minbet and you can raise as if you was going to cbet normally. But remember to see what they do this with when they are at showdown.
when its correct to donk:
1. when a reg spaz's out due to donk bets (a lot of regs actually do this because they see donking as weak because who donks with the nuts right? (obv dont go overboard with this, its about finding which reg does that and exploit, obv not many at 2nl will tho))
2. When you have a set and the board is very drawy, e.g. you have 7's on 678s and you dont want to give free card.
3. When the pot is multiway and there is a fish inbetween you and a reg. A reg should be playing fairly straight forward (cbettin for value, checkin back air, as there is a fish in the pot, and checking to them gives the fish a freecard and you potentially miss value from it)
4. When a reg often checks back decent Showdown value hands on the flop and is generally quite passive. (you find these more the lower the stakes you are) so obv you want to be doing this with TPTK type hands on semi-drawy boards
i think anyway
,