if he asks about your personal life ( if you have a bf, ever been in love? etc.), and if he seems interested in spending time with you. However, if he's like that with all the girls, he's just a player.
haha, you don't. just ask him or talk to him about it. Or, you can try to make a move on him, if he takes it either he likes you or is a dirty idiot. Either way, you still don't know unless you straight up ask him or he straight up tells you.
(Coming from a guy)
If you thik he likes you, and you're into him too you should ask him, but if you don't want to be really obvious you could flirt with him 2 see how he responds. If u think he responds in a positive (like you think he likes you) way, go ahead and ask if he likes you or ask him out. If not, don't worry about it. If he doesn't already like you you can change that...flirting, 4 example. If you're not that into him, you should forget it if he's not into you because he thinks of you what you think of him and that's it. Good luck!