I've watched him a fair amount and I'm a bit of a fan, so I'll oblige with a short summary.
His passing generally is great. Long or short. He has great vision and plays incisive forward passes, mostly along the ground, but also comfortable with some over the top balls. Very capable of unlocking defences. That's not the reason his numbers are high though, it's because when he's in possession he likes to keep shifting the defenders around by playing simple close range passes until space opens up or one of his forward players make a move. So a bit like Mata does some times, he just plays the ball to a teammate 5m away, move himself 2m, receive the ball back, do the same with another teammate etc. So a lot of the time he's not moving the ball forward but he's moving it around until he gets an opportunity to pass it forward. That's why he clocks so many passes.
This might sound underwhelming but it's necessary to his play because (and this is why people have major doubts about him in the EPL) he's not physical at all. He's got a Lingard body type, albeit slightly taller, but he's neither fast nor does he have great stamina. You often see him huffing and puffing from 70' onward in games and get replaced by Diawara. And because like Lingard, he doesn't do well under physical pressure it's necessary that he moves the ball around constantly so that he's never really physically pressed and have to shrug players off. To be fair to him, whenever he receives the ball he nearly always has a short option in mind, so if a player tries to rush him he will simply pass and move, so he doesn't get dispossessed much at all despite his lack of strength or pace. However, the fact the all Napoli midfielders and defenders are very comfortable with the ball at their feet is also conducive to this play. He doesn't have to worry that a teammate receiving the ball will panic and hoof it or lose it.
So yeah, he's a great midfielder for Napoli in Italy and a highly intelligent and skilled player. But unfortunately he has some physical limitations that I think prevent him from being great. He will often get omitted from the starting XI if Sarri feels the team will require the strength, agility and aggression of Diawara more in that particular fixture. Both of them play at the base of a midfield 3, but Diawara is more of defensive destroyer and Jorginho more of the passing metronome. So they are used depending on the situation.