What does his squat mechanics look like compared to ideal squat form?
With several knee operations he has tolerance for silliness or less than ideal mechanics.
He may not be able to buffer deviations in technique that he may have been able to buffer in the past.
What has he done to address the knee?
up/down stream of the knee to feed slack to the knee?
Episode 348: Restoring Knee Motion After a Tweak

Pro Episode # 46 – The Box Squat:  Knee Function, Rehab, Pain, and Pathology 
Episode 33: FGB Push Press Prep ; Hot Patellar Tendon: Hip /Calf/ Hamtsrings
Pro Episode #5 – Knee Stability and Laxity
Voodoo Band Your Patella Femoral Pain
Episode 344: Compression Tack and Floss–The Knee
How is his ankle mobility?
Foot position when standing/walking?
Wonky, Beat Up Joint? Feed That Thing Good Mechanics and Some Slack