The matter of translating Polish "człowiek" to English "person" is difficult. I wrote something about it here: https://www.duolingo.com/comment/19428542
I think this is one of those situations when I wouldn't accept it. "Jesteś człowiekiem?", after all, is like a phrase from a sci-fi movie.
After reading your other, lengthier comment, I still don't see why "person" is marked wrong here. "Are you a human" and "are you a person" are both strange questions, like something one would only hear in a sci-fi movie. And you say in your other comment that człowiek is more commonly used than osoba. Well, "person" is more commonly used than "human" (especially as a noun). So, again, why wouldn't it be used here?
I discussed it with a native that helps us regularly, I actually expected her to agree with you, but she's against accepting it. Basically, "person" and "człowiek" overlap, but are definitely not the same. A person doesn't have to be human. Okay, obviously we enter sci-fi mode now, but if an alien asks you "Are you a human?", this alien is clearly a person as well but not a human. Similarly in comics/animations with antropomorphic animals, they are persons as well. I know that rejecting 'person' annoys many people, but I still think it's worth pointing the difference between "człowiek" and "person".
The noun "human" or, even better, "human being", refers to the one of the biological species of the animal kingdom. In this context the word "person" does not make sense, because "a person" might be, for example, a totally abstract character played by an actor in a play or a movie.
human/human being - istota ludzka, przedstawiciel jednego z gatunków całego królestwa zwierząt, istota, która należy do gatunku homo sapiens
Are you a human being?/an animal?/a robot?/an alien from another planet? -
Jesteś człowiekiem?/zwierzęciem?/robotem?/przybyszem z innej planety?
Nie chodzi o pojedyncze osoby, ściślej, pojedynczych osobników gatunku, lub przedstawicieli gatunku, lecz o cały gatunek ludzki, który z punktu widzenia biologicznego jest mięsożerny, w odróżnieniu od krów, które są roślinożerne.
Humans eat meat - Gatunek ludzki je mięso/Gatunek ludzki jest mięsożerny
Both questions have the same meaning, and "Czy" is not required by any special rule of grammar. But, in spoken language, the question "Jesteś człowiekiem?" might be mistaken for a statement when it is hard to hear
the intonation... In writing, you know it is a question only because of the question mark.
The sentence started from "Czy" indicates right away that the question
will follow, so the intonation typical for a question is not that important.
Not directly, no. It can be translated this way in many sentences (let's say "On jest dobrym człowiekiem" = "He is a good person"), but not when "człowiek" is about... well, species.
See this comment: https://forum.duolingo.com/comment/19428542?comment_id=19447331