Chauvin had two knees on him at one point? Or are you referring to Keung's knee on his back? I missed the trial today but I'm catching up now.
At one point Chauvin kept repositioning his knee and applying more pressure by leaning forward and pressing his knee down further. At the same time Keung had his weight on Floyd's back. This was right before Floyd appeared to stop breathing and was unresponsive. (Also when the bystanders started sounding more and more urgent. Chauvin pulled out his mace and aimed it at them.) Keung removed his knee, but Chauvin kept right up until the paramedic told him to move.
Chauvin had BOTH knees on GF. Left knee on his neck. Right knee above shoulder blade.