A win is a must for Juventus. They can easily climb up as long as they take three points from Milan soon. They shall focus on how to beat their next opponent, and may be struggle to do that.
Juventus's gap to the Napoli is very thin. They can climb to the first position when their opponents will miss three points soon.
I haven't seen a rumor about Juventus's January transfer to buy a new player, but they will sell Fagioli for 25m.
Not only Juventus can shift Napoli from its first rank even though it can win against Milan because the teams above Juventus also have a small difference in points if they all win then Juventus will remain in its current rank, but if Fiorentina, Inter Milan or Lazio lose or draw then Juventus has the opportunity to rise, but the match between Juventus and AC Milan also cannot be said to be easy because Juventus' performance is not completely stable and has experienced more draws I think in this match it could also achieve a draw.