I am getting a shooting pain in my right knee only when kneeling on it, it's very sharp and painfull, otherwise my knee is fine . what is the cause?

Probably bursitis: Knee pain especially on kneeling is suggestive of bursitis most likely prepatellar bursitis. There are numerous fluid filled sacs on the knee joint that help lubricate it. Sometimes they get inflamed. Rest and and applying ice can help. A consultation with a physician may be warranted to do further work up such as ordering x-rays to rule out possible fracture.