How do I ask his number?

Well, what makes you more comfortable? Either one works however, given that you are in the same university, maybe asking for coffee is more ideal. Do you have a class together, or do you see him around? Either way, you can say, 'hey, I'm going to the coffeeshop, to get coffee/juice/whatever. You want to come? ' if he were to say that he can't go for whatever reason, immediately you can follow with, 'thats too bad, but if you ever want to go, let me know. '
the reason I don't suggest the phone number is because once you get it, do you plan to call right away? Also, a lot of guys are not so good on the phone, and many times, they don't know how to talk on the phone; getting him to go for coffee gives you more of a chance to talk to him. Plus, that might be his hint for him to make a move.

ohkaye ooh I love this question

if your in the universty

just hang out and when yall hang out

just straight up ask him

be like ohkaye well ill talk to you tom.

and can I have your number and we can meet up again sometimes

thats how I get numbers

ill just roll up and ask

or ask when some specail event is happening and say ill call you