[DISCUSSION] Guys I have a very important question

[Excalibur0126]

It tells you, but sometimes it's holding an item which blocks the ability. So you just have to catch it and look in your PC/Party to see if it has the right ability. Remember, the more you encounter the Pokemon, the higher chance it has of having its hidden ability.

EDIT: For Kakuna, the only way to tell if it has its hidden ability is to breed/evolve it.