There are two men named "Jules" in Stutsman County, North Dakota. Perhaps one is the father...? DNA tests of their descendants (if any) might help.
Update: One is 58 (might be unlikely?) but Jules Hagensen was 42 in 1920 (more likely.)
Update: Jules Hagensen's name was Julius, according to a newspaper account. He was single, living with his single housekeeper, Tina Lorenz, age 22 in January 1920, by February 1920 he was married to Marie Florentia Lorenz (most likely the same woman.)
Julius Hagensen seems like an excellent candidate to me!