according to spoilers yes
It's been implied in previous chapters
There were a few chapters where we learned what happened to pavel in the different timelines, and we learn then that yes, he knows
He knew from the start.
When Sion first saw Parvel after he switched bodies with Siennas, Parvel entered the room and Sion (in Sien's body) called his name Parvel knew from that moment that it was Sion and not bloody siennas.
Does pavel know that sion is sienna's body? I just really wanna know