I get random sharp pains in only one of my knees, what could this mean?

Needs evaluation. Sharp pains in the knee joint can be benign or may indicate something more serious like a torn meniscus (cartilage). This is not something you can diagnose on your own. Your doctor can find the answer by doing a history and detailed exam, and may order additional tests such as an MRI or x-rays.
Many reasons. It could be tendinitis, arthritis, meniscus tear, or loose body. Get checked by an orthopedic specialist.