Some other spellings you'll want to consider are Knüppel Knüpple Knueppel Knuepple & Knippel. These variations are found in "Milwaukee's German Newspapers; an index of death notices and related items" (1844-1950).
poster says: "... but it was pronounced Knep - lee ..."
Actually, probably pronounced Knep - leh
Gary Rebholz, compiler/editor
Indexing Milwaukee's German newspapers continuously since 2007... helping family researchers find the evidence of our collective historic German-American families & culture.