Barcelona and Napoli have not won their last match in their respective leagues so it is a bit difficult to guess who will win. However, because Barcelona are playing at home, they must be able to use it to play better than Napoli. Had Barcelona won, I'm also sure they wouldn't have scored more than 2 goals in this match. There are good expectations from Adama who is currently in good form at Barcelona.
I really don't think that the teams not winning their last match in their own League proves anything. Because if we actually want to make any assumptions we have to look about at least the last five games. Judging by the last five games I would say that Napoli is performing better than Barcelona. But this match will be a home match for Barcelona so I think Barcelona will obviously have some advantage over Napoli.
On the other hand, Barcelona will also be really motivated to win this match because this will be a big restriction on their path to winning the title.