Well, depending on the context, it can mean: I like you. (romantic) I like you. (platonic) Or it can mean that the person likes something about you. Maybe your clothing style, your attitude. In a question, it can mean, "Do you understand?" "Ya dig?" "Can you dig it?" It's a slang expression, and not very common anymore. When I was younger, it was much more commonly used.

It could be romantic or not. To a love interest, it's basically a way of saying "I'm interested in you." Non-romantically, it means more like "you're cool". It's not necessarily commonly used, and is usually used more toward a love interest, but it's old slang and I don't think many people use it anymore

Well, it's an old expression, "To Dig Someone/Something," which means "To Understand/Like Someone(/Something)." Well, it's rarely used now.