If you read up you’ll find a ton of articles on T Nation about training abs.
This is like asking how to train your biceps or any other muscle. Neither I nor anyone else other than you knows your muscle fiber make up, what your body responds to. Some people grow legs in the 5-8 rep range others sweat by 12-20. Some prefer mechanical tention, others m-tor activation, and yet other lactate build up (this last one might be called something different).
Since you want abs I’ll assume you are in reasonable shape, because no matter what training you do, you won’t know if it works if you can’t see your abs. If not, start there.
Then if that’s all good, try different things. Things that generate intra abdominal pressure work well, like carries or zercher holds. Anti rotation like pallof presses, flexion exercises like crunches, banded standing crunches, leg raises and the million others can work, see what feels right. Personally, full sit-ups kill my lower back so that’s a no go for me. Rep wise, low with added weight, high reps, timed sets, paused, slow eccentric, and a ton other ways.
I don’t know your training background, your experience level, but there are phases in my training when I do some kind of ab work almost every day. Other times maybe once or twice a week. Occasionally might give them a rest for a few weeks other than the big movements.
Take your pick, try things…