My first Italian knish, earlier this month at Ferragosto, traced its origins to Brownsville, Brooklyn. Back in the day, when "Brownsville was a veritable melting pot of many ethnicities," a neighbor's shared knish recipe was modified with Italian fillings. I've since learned of at least one current New York pizzeria that does much the same.
For this street-food version, a standard knish is sliced open, then dressed with griddled onions and peppers ($3) and an optional segment of sausage, hot or sweet ($2 more). In other words, here the knish itself stays the same; a familiar Italian sandwich is transformed by dispensing with the bread.
D'Angelos Italian Sausage
Encountered most recently at Viva La Comida!
As a habit, parked Monday through Saturday, 10:30-6:00, on Woodhaven Blvd. outside St. John Cemetery, Middle Village, Queens