I'm a college-level volleyball player with weak ankles. I trained extra to prevent ankle injuries and ended up hurting my knee. Am I just prone to injury no matter what I do?

Some people do seem more likely to get injured than others. This could be related to an overactive nervous system, lax ligaments, or poor joint position sense. There may not be an easily identifiable link, or there may be more than one factor involved.

In your case, it may be that training for the ankles worked well. You didn't injure your ankles and they were able to with withstand outside forces. It's possible the knee joint was stressed instead. When the ankles are strong, forces from the ground up through the
foot and ankle are transferred to the knee instead. Injury can occur here if this is the weakest link.

It may be best to keep training for improved ankle strength and improving the joint's sense of position (called proprioception). An overall program to include ankle, knee, and hip may be best for you. If you need help, seek out the assistance of a Physical Therapist or athletic trainer.