Ask her. Or ask around among others who might know. The first idea is more direct.
If u like a girl who already has a boyfriend but you dont know if she likes you or know,the first thing you have to do is that you will have to make friendship with that girl and if she is already your friend,then increase your friendship and one day confidently ask her that what does she feel about you..
Treat her better than her boyfriend does.
try to brake them up :)
wait until she breaks up with her boyfriend and then make your move
give it a shot
Patience. You shouldn't expect her to like you as a boyfriend if she already has one but you can still be a non boyfriend.
If he is already your boyfriend, he must like you.
I know you have a boyfriend but I really like you. It's as simple as that:) no joke just tell her!!!!OR just don't tell her at all. it'll just make her feel awkward around you because she knows and she already has a boyfriend.
act mysterious and give her a sign
Does the girl know you like her? How long have you an and your boyfriend been together? And are you asking what should you do?
try to impress the girl if that doesn't work sorry shes gone
Ask her friends in a subtle kind of way. Don't stalk her or follow her around! If you're brave, ask her yourself!