I have sharp pain while kneeling on my left knee. It feels like a piece of glass stabbed me followed by some numbness. Its below knee cap to the left.?

Several thoughts. Pain below your kneecap area which is the patella tendon can be caused from inflammation of the patella tendon. It can also be from arthritis under the kneecap. There are also skin disorders and bursitis that can cause pain in this area. You really need to get a good physical examination to be able to make the true diagnosis. Seek out the advice of an orthopedic surgeon to help you.
Need more info. The possible cause ranges from bursitis, tendonitis, loose or foreign body, neuroma or problems within the knee joint.