In trapoline jumping, the knees are held rigid. Pain would usually be on impact. If this is the case, then it indicates that the knee joints are being compressed. It would indicate a “crushing” together of the upper and lower bones in the knee joint.
This may be due to a loss of cartilage between the bones of the joints. Try glucosamine chondroitin to supplement the cartilage of the joints. Foods containing collagen would also help.
If the pain is felt jumping or rebounding upwards, it would indicate a painful stretching of the joint muscles. That means that the joint muscles are extremely tight. Relax the muscles by taking a hot shower or drink some wine to relax the muscles. Muscle rub would also relax tight muscles.