Stating the obvious, but the key against Napoli is stopping their left side.
The movement from Insigne, Hamsik and Ghoulam is good and and awful lot of Napoli's goals come down that side.
Most teams fall into a trap of indecision between whether to mark or whether to close space and Insigne and Hamsik often take adavantage of that.
If Insigne goes inside, does Lichtsteiner track him? Does he become Sturaro/Marchisio's responsibility? Does he become Bonucci's responsibilty? Or do all of them hold shape and try to keep the space between them as small as possible?
And who is responsible for Hamsik if Insigne goes inside and Hamsik loops outside him into the space Insigne had left?
I think I'd be playing something along the lines of the system above, possibly a bit closer to 4-3-3, and going pretty close to man-marking down that side.
Lichtsteiner-Insigne
Sturaro-Hamsik
Cuadrado-Ghoulam
The movement isn't as good from the other Napoli players, nor is there a consistent end product from them (aside from Higuain, but that's normal for the central defenders to have to deal with) so I wouldn't be marking elsewhere.
This stuff is of course when Napoli have the ball.
Juve can play pretty aggressively, I think and push the fullbacks forward because Insigne and Callejon will track them.
Great chance for Dybala to be influential in this game because Jorginho is Napoli's weak link defensively. Allan should be preoccupied with Pogba and unable to help Jorginho much.
No reason for Juve not to try and make the pitch really big and focus on threading balls through the midfield to Dybala's feet.