Depends on the axie, its age and size, water temp, gender and foodstuff.
Juvies (under 6") need feeding daily, bloodworms until they are 3+", earthworms after that.
Adults you can work out a plan that suits you and your axies. I feed mine daily, one worm each, but you can feed them twice a week if you feed them a bigger meal. Axies at 20C need more food than at 10C. Females need feeding more when producing eggs, less if not breeding. Axies healing after an injury need more food.
You need to be guided by your axie's appetite and shape, feed enough to keep their belly as wide as their head. Feed mostly earthworms.