you are Italian, so there isn't difficult to explain you the difference.
Pršut stands for the "prosciutto di San Daniele" type of ham. The most typical representative of this group here in Slovenia is "kraški pršut" (prosciutto di Carso), which the four major producers from Kras region tries to protect its origine. I hope they succeed soon. Kraški pršut suppose to be made of pig legs of Slovene origine. Legs are salted with sea salt, then slightly smoked using local juniper wood and finally put aside on the heavy carstic bora wind to dry them.
Šunka is everything else. I mean, every other result of processing pig bottom legs.