Minho, don't you know that tall, skinny female student whose name is Jisu?
민호씨, 지수라고 왜 키 크고 마른 여학생 알지?
I think 왜 in this sentence will throw many people off. In this sentence, 왜 means 그 (the or that). i.e. 그 여학생 (the female student or that female student).
민호씨, 그 키 크고 마른 여학생 알지?
Also, 지수라고 is from 지수라고 불리는 or 지수라고 불리우는. "~라고 불리는" translates to "who is called ~" or "whose name is~."
지수라고 불리는 학생: A student who is called Jisu. A student whose name is Jisu.
천재라고 불리는 남자: A man who is called a genius.
민호씨, 지수라고 불리는 그 키 크고 마른 여학생 알지?
Hope this makes sense.
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As a side note, you will sometimes hear an expression like "왜 그 예쁜 학생 있잖아." We use "왜 그" at the same time, too. (the same meaning).
i.e.
왜 그 못생긴 여자: that ugly woman
왜 그 예쁜 여자 있잖아, : You know, that pretty woman,
왜 그 똑똑한 남자 있잖아, 작년에 의사가 됐어. You know, that smart guy, he became a doctor last year.