Injury 2 left knee, ankle. Ankle problems 6 mo later. DX PTT focus on pronation unrelated 2 fall. No problems w/feet wore orthotics. Why this DX?

Biomechanics. Your knee pain, based on the limited information given, may be due to/exacerbated by the biomechanical issues related to posterior tibial tendonitis/dysfunction.
Need more info. Unfortunately not enough information is given, to give a definitive answer. Where is your ankle pain located, is one foot/ankle more pronated or collapsed than the other, is there weakness or difficulty to raise up on your toes. These things and others must be evaluated to give you an answer.
Tendonitis. The posterior tibial tendon comes down the inside aspect of the ankle and inserts on the inside undersurface of the foot. If you have a flat foot lack of support and overuse can cause the problem. Left untreated it can lead to a dysfunctional tibialis posterior resulting in a collapse of the foot and a major problem.