Jenny: I eat snack at when i want to eat.
Correct: I eat snack whenever I want to eat.

Hello, Jenny! Ah, so you passed your answer as your homework. Thank you
for the answer! That's why you can't say the time. It's because you eat
snack whenever you are hungry. You sure eat a lot!

In your sentence, we do not put the word at anymore because we didn't put the time.
We use the word whenever to indicate that you eat "anytime".
When we write the pronoun I, we should always write it in capital letter.

Take note of the correction, Jenny! Thank you. I'll see you in class!

~ Teacher Mary