Jean-Clair Todibo, Nélson Semedo, and Arthur are the ones that could go from the Camp Nou to Italy, while Miralem Pjanić, Daniele Rugani, Cristian Romero, and Mattia De Sciglio are mentioned as candidates to leave Juventus and go to Catalonia.
The Arthur-Pjanić swap has been discussed at length, but it is not the only possibility in the deal.
Semedo and De Sciglio could swap places, although it is understood Juventus would have to add a lot of money on top to make it so.
Todibo could go for Rugani or Romero. In all cases, we are speaking about backup centerbacks as both teams (especially Juve) consider themselves well-stocked in the area.