This is one of the earliest European card games whose rules can be reconstructed with some confidence. It dates from the early 15th century and is one of the first trick-taking card games in which there is a "chosen" suit some of whose cards have the power to beat cards of other suits.
David Parlett's Karnöffel page has a history of the game and a reconstruction of the rules.
Another reconstruction of Karnöffel can be found on an archive copy of Glenn Overby's Karnöffel page.
The German language Landsknechtsportal (archive copy) includes an illustrated history of Karnöffel and a partial explanation of the rules, which (as of September 2007) dealt only with the betting and scoring, reconstructed by analogy with the modern Swiss Kaiserspiel, not the ranking and play of the cards.