"He can cook."
Translation:Он умеет готовить.
уметь specifies the ability to do something. Он умеет читать = He can read (he has the ability to read, he knows how to do that); Он может читать = He can read (because he has the time, he's not busy).
Without more context, он может готовить should probably be accepted. It's not too hard to come up with an appropriate situation: "he has an hour today to do something, what can he do? He can read a book, he can wash his clothes, he can cook." Usually you'd specify what he is cooking, though, and not just the action itself.
If you wrote it in the English alphabet, then it transliterates to Он умеет готовит, which is improper verb conjugation. Готовит means he, she, or it "cooks." In this exercise, the verb is in the infinitive perspective "to cook," so it must be готовить. That "Ь" must be at the end of the verb to be correct.
Приготовить is the perfective verb that means to make food at a specific time and place. "He can cook" has the broad, general sense which requires the imperfective verb готовить. English doesn't have perfective/imperfective verbs, so it can be difficult to understand this concept.