Here is the classical definition of how to cook it from Larousse:
Soaked the leg in cold water for 3 hours, and then scrape all hair off the skin. Prick the leg in a few places to allow fat to drain while cooking.
Wrap and tie it in a cloth, and simmer in water for 3 hours.
Served hot with a purée of potatoes or lentils, or serve cold in slices for sandwiches.
The word “Zampino” comes from an Italian word for “leg”, “zampa” (usually “gamba”.)
Zampino is often confused with Zampone Sausage, because some parts of Italy call a “Zampino” a “Zampone”, and some call “Zampone Sausage” “Zampino Sausage”
Larousse even gets confused, because they call the above recipe “Jambe de porc farcie” (“farcie” meaning “stuffed”), although there is clearly no stuffing happening anywhere — that is Zampone Sausage.