as a Sentence Ending Particle denotes a very strong #male question.
It almost sounds like an accusation.
Very often together with explanatory の・んだ
この焼きそばを食べたいのかい？ Do you want to eat this yakisoba?
彼女は奇麗なのかい Is your girlfriend pretty?
大学生なんかい？ 中学生だと思った。 You are a student? I thought you were a middle schooler.