"Again?"

Так, це неповне питальне речення. Вирване з контексту.

Yes, it can often be used to ask someone to repeat something (we would understand it like "please can you do that again?"). Or if you say it in an irritated voice, we would understand it to mean something like "why are you making me do this again?" (maybe after Duolingo has asked you to translate the same sentence 5 times).