Do you have to be in China to study abroad? 这句话是询问 “出国留学必须在国内吗” 的常见英语表达方式。
如果你想更详细地询问相关情况，比如询问办理留学手续等是否必须在国内，还可以说：Do you have to be in China when applying for studying abroad or handling relevant procedures?
要是想问关于准备出国留学的一些事项是不是必须在国内完成，也可以这样表达：Do all the preparations for studying abroad have to be done in China?