Women are emotional beings. Their emotions give them away and its nothing difficult knowing when they like or are attracted to you. However, ladies could be very pretentious about their emotions. They always want to play safe. So knowing their feelings
First, notice her reactions anytime she's around. Ladies can hardly hide it from their expression when they like a guy. She'd try to make eye contact with you ands be watching to see if you'd be staring at her.
Secondly, you can watch out for her body language. If you both are sitting close to her, watch the way herself body angles. If her body angles towards you, it's a clear sign she's interested. However, if she's angled away from you, she MAY not be interested in you. Also, if you are sitted opposite her, she will unconsciously move her feet towards you, otherwise, she'd put her feet underneath her chair.
Also, if a lady is interested in you, she'd be quick to laugh to any joke you make even I it's its not so funny. She finds you interesting enough.
These are some of the few ways too know emotional attraction. Watch out for this and see how the magic works.