询问某人学习的专业时，可以使用以下英语表达：

直接询问

What's your major？

礼貌询问

May I know your major？

Could you please tell me your major？

Would you mind telling me your major？

替代问法

What do you study in the university？

Which major are you pursuing？

这些表达方式可以帮助你礼貌且有效地询问对方的专业。