The 1919 New Haven city directory has this:
Fredenberg, John W., employee Railroad, home 150 Rosette
The 1920 New Haven city directory has this:
Fredenberg, Catherine, widow of John W., home 150 Rosette
That address matches the address for the 1920 census listed above with Katherine Fredenberg & daughter Kathleen.
Given the time frame, I think the 1919 death is more likely the John you're looking for.