What happens if the non-striker, holding his gloves, drops one of them and the ball in play touches it?

I find no Law that specifically describes what would happen. However, it is a common convention that if the ball strikes a batter or their bat when running between wickets (so say they got between the fielder and wicket keeper and the ball deflects off them) then they do not run additional runs. If the contact was not intentional, they have the right to in the rules, but most batters will not take the extra runs. I suspect the same would apply here if the deflection off the glove was significant.

Note that if the Umpire deems that the batter deliberately obstructed the ball using their glove then they would be given out Obstructing the Field, however I assume you mean that the contact is accidental.