正确的是which class are you in。意思是你在哪个班？
class
英[klɑ:s]
美[klæs]
n. 班; 阶级; 等级; 种类;
vt. 把…归入某等级，把…看作（或分类、归类）; 把…编入某一班级;
adj. 很好的，优秀的，出色的;
[例句]My class has fifty pupils.
我们班有50个学生。
which的用法如下：
1、哪一个；哪一些
used in questions to ask sb to be exact about one or more people or things from a limited number
Which is better exercise─swimming or tennis?
游泳和网球，哪种运动比较好？
Which of the applicants has got the job?
哪一位应聘者得到了这份工作？
Which of the patients have recovered?
哪些患者已经康复了？
Which way is the wind blowing?
风朝哪个方向刮？
2、（明确所指的事物）…的那个，…的那些
used to be exact about the thing or things that you mean
Houses which overlook the lake cost more.
俯瞰湖泊的房子要价高些。
It was a crisis for which she was totally unprepared.
这是一场她完全没有防备的危机。
3、（进一步提供有关某事物的信息）那个，那些
used to give more information about sth
His best movie, which won several awards, was about the life of Gandhi.
他最优秀的电影，就是荣获几项大奖的那一部，是关于甘地生平的。
Your claim ought to succeed, in which case the damages will be substantial.
你的索赔应当能成功，假如这样的话，损害赔偿金将会相当可观。
Which class are you in?你是哪个班的？
回答是:
I am in Class 1，Grade 2.我是2年级1班的。本回答被网友采纳
which class is are you in
你在哪个班？
你是哪个班的？