There is a sharp pain in my toe knuckles. It feels like I have to crack them, but when I do the pain doesn't go away. What could it be?

Osteoarthritis. Possible osteoarthritic changes at joints in toes. X ray examination should rule this in/out.
Early arthritis? Sharp pains in the toes at your age would seem out of the ordinary. The feeling of having to "crack" the toe joints with pain may indicate that you might have some accessory bone inflammation or some sort of tendon issue/ligament issue at the joint level. A proper foot orthopedic examination should help diagnose the problem.
Inflammation. Most probably this is due to inflammation to the area that may be due to wearing a lot of sandals where you have to curl your toes to grab the ground or sometimes due to exercise shoes or jumping. Consult your podiatrist for the exact cause of this condition.