It's simple. First of all, you should take the initiative to ask more questions to make him like you. Then, slowly try to talk to him about employment and other topics, so that you can get familiar with him a lot, and if you can, you can also talk to him about other topics. Contact a few more times, QQ should be no problem. If he leaves after class, but he has an office, you will be more impressed if you ask in the office. Of course, don't ask him for it on the phone. After all, it's not appropriate.

This is just my humble opinion for reference only.

Finally, I wish you and he become good friends!