J. Knoszvitch (French: J. Kroïszvitch) is a Syldavian waiter who appears in King Ottokar's Sceptre in The Adventures of Tintin series. He is first seen as Tintin and Snowy enters the Syldavian restaurant Klow to search for the man whom with Sporovitch spied on them along with Hector Alembick about their journey to Syldavia. Knoszvitch noticed them coming in, and offered the menu to Tintin. As Tintin ordered szlazeck and mineral water, he asked him where to wash his hands, intending to find the agent. He shows Tintin the door and told him to go to the right. Tintin listened, and took left instead. Koszvitch found him upstairs, and showed him menacingly to the right direction. He was also seen talking to the agent about Tintin and Snowy entering the restaurant.
As Tintin orders a check, he gave him a receipt to pay the bill. Tintin reads the bill as he reads, "Danger awaits he who pokes his nose into other people's business." He asked Knoszvicth what the bill means, and he explained that it's just a proverb or a motto that's being used as old Syldavian custom. His full name was revealed on the receipt. As to szlazeck, he explained to Tintin it's a specialty, as it was the name of the young dog. Tintin was surprised to hear it, and found Snowy. He sees them leaving the restaurant nonchalantly, and laughs to himself, until he sees kitchen ruined as it appeared to by Snowy eating all the food.