trivial term of endearment, by 1910, from the name of the baby added in 1907 to the popular "New York World" comic strip "The Newlyweds" by U.S. cartoonist George McManus.
The name is perhaps from Snooks, proper name used in British slang for a hypothetical person (1860; compare Joe Blow in U.S.). As an actual proper name, Snooks dates back to the Domesday Book and may be from Old English *snoc "projecting point of land" (perhaps here with sense of "big nose").