"Is he a track and field athlete?"
彼は陸上選手だ would be the common casual form. I am not completely sure, but your option might also work. See here: https://japanese.stackexchange.com/questions/514/what-exactly-is-%E3%81%AA%E3%81%AE-nano
Sorry, I overlooked that it is a question. Then, removing だ with an intonation shall do according to here: https://www.wasabi-jpn.com/japanese-grammar/question-markers/
なの should also work then.