I landed on my kneecap while diving at volleyball. I then later dove and something popped when I got up. What should I do and can I avoid a doctor?

WeAR knee pads. If you can walk on it and it had full ramger of motion and no swelling or bruising, ice it and followi t go to doc if it dosent get better quickly it can wait a day use your best judgement.Have your team trainer look at before practice.
Ice. Ice the knee. If you are unable to do a straight leg lift you need to see an md asap. You can try gentle motion and leg lifts. If there is any significant swelling you need medical attention.