Is the only way to get fat in the knee area is to gain weight ? because i'm skinny and you can see my knee bone unlike others who are bigger.

A bit of an odd: Request. You are right, without a invasive intervention, there is no way to cause a "spot" gain in fat distribution. Remember your quadriceps muscle attach in and around the need, so increasing the size of these muscle(like that vastus medialis-the big tear drop muscle at the inner upper aspect of the knee) can improve the "size" in the knee area.

Bony knees: Try exercise. As the muscles become more developed around your knees the bones will appear less prominent.