Alan McGowan: Ancestry.com has the following marriage record:-
Walter Hugo Albert John, an 'Apotheker' (pharmacist, John's known profession) married Julie Gehrmann in Frankenberg, Saxony on 29 December 1910. The document records John's birth information as 29 January 1879 in Sandomierz, 'Russland' (later, Poland), as that area was still under Russian control at the time of his birth.
A 1915 record shows him living in Breslau (Wroclaw).
Ranneforths Schach-Kalender 1920 shows him residing in Berlin. He appears in later editions of RSK at Emser Strasse 40, Berlin W15, and this is the address for him in the 1943 Berlin Address Book.
The Wikipedia entry for Walter John offers no sources for his date/place of birth or his death, stated to be December 1940, Berlin.
The German researcher Peter Anderberg has previously shown elsewhere that Schach-Echo of 10 June 1942 had a report of a simultaneous exhibition by John in Posen on 1 May 1942.
John was associated with the Kraft durch Freude (Strength Through Joy) state leisure organisation. He played in regional tournaments and gave exhibitions organised by the group in Germany and occupied Poland. In 1940, for example, he played in several KdF events:
Zoppot: John (Berlin) 6½; Rogmann 4½; Ahues and Elstner 4 and four others.
Berlin: Elstner 7½; Rogmann 7; Hartmann and W. John 6½.
Leipzig: E. Grünfeld 6½/8; W. John and Rogmann 5½; Elstner 4½; Heuäcker 4; Kübart 3½; Zollner 3; Ulrich 2; Wacker 1.
(Deutsche Schachzeitung 1940, pp 158 & 187.)