how parents know about the children interest, likings.. if parents know their child's interest then how to handle it or respect it or guide the child in their own way?

When the child is 3 or 4, they are not exposed to activities and games other than what you tell them or they get to learn in the day care or preschool. You have to give them time to figure out what they like. If you send them for say, a drawing class and you see them doing it often and home and see them excited about the activity, you know that the kid has interest in it. And when you figure that out, you can enrol the kid in drawing classes. Same happens with any activity, dance form, sports etc.