I've been a positive player in Spins and Fast Fold microstakes, so I figured I would play some tournaments to see if the field is as soft as people say.
Although it really is soft, I realized I'm one of the people who make it soft, as I have no idea what to do post-flop in very common situations

It was a tournament with 7 minutes per blind level, 7-max. Only 0,33c buy-in.

With 50 bbs, early in the tournament, I had J5s in a 33J rainbow flop, and someone who participated in some hands and c-betted, donk-betted bigger than his usual, 75%, in this flop, which ended up being like 6 BB. Preflop someone else was the agressor for 2BB, had two callers (me from the big blind), he was in the small blind and then he donkbetted. How should we play this hand?

Second situation, most people with 30 BBs including me, I had 88 from CO and raised 3,5 preflop (because of one limper), two callers, flop 467 two-tone, one opponent donkbets full pot.

Third hand, I didn't take notes of the preflop situation: 30 bbs, i have KQs, flop K74 rainbow, they check, I bet 30% pot, they raise all in.

Fourth: J2789 (3 clubs) and I had a Q-high flush, two opponents go all-in on this river, we had about 20 big blinds.

Hmm. These might be a little tricky since at stakes this low you're going to see a lot of odd play, but I'll do my best.

Hand 1 - I'd just fold, you have two people to act behind you and this is a pretty dry and static flop. It doesn't really make sense for him to be doing this with less than a better Jx than yours. Maybe he's just off his rocker and blasting at a board he thinks everyone missed, but you can't assume that and you don't even close the action to see what he'll do on the turn.

Hand 2 - where the callers are and which player donked out matters, but at these stakes and with the pot already as big as it is I probably just get it in and expect to see a good 7x or some kind of pair and straight draw combo a substantial amount of the time. (Which is a great result for you with 88 if they have 75/65/54 type hands, because you block the top end of the straight and their two-pair card gives you a straight.)

Hand 3 - Again, the preflop action and the size of the pot really matter here. Absent other information though I just get it in; you'll see worse Kx and 65 a lot.

Hand 4 - Again, here's where the size of the pot and the actual action matter. There's a big difference between you betting last to act, getting check-raised all-in, and then cold re-shoved, vs. if the first guy to act shoves and the second reshoves. And there's a big difference if the shove is like 2/3 pot vs. 2x pot. In general at these stakes I probably stack off because with the four-straight I wouldn't be surprised if at least one of them has Tx (or even 65) and we beat a lot of flushes.

In the future, try to include as much detail as you can in each hand, because the action before the decision point and the size of the pot really matter to answering these questions.