Would like to learn the military service for German Jewish soldier, Caro W. Naphtali, of the Imperial German Infantry 124th Regiment?
Please see my answer on How to find information on German soldiers from World War I and World War II? for general research strategies.
I did not find Caro Naphtali in the Verlustlisten, so – if the spelling is correct – I assume he did not die during the war and wasn’t injured or taken prisoner.
There is secondary literature available for the unit, which should give a general idea on battle participations e.g.: Wolters, Gerhard: Das Infanterie-Regiment König Wilhelm I. (6. württ.) No. 124 im Weltkrieg 1914-1918" - Stuttgart, C. Belsersche Verlagsbuchhandlung, 1921 (online)
The regiment was from Wurttemberg and belonged to the XIIIth army corps. The musterrolls are available via the Hauptstaatsarchiv Stuttgart (details: https://www2.landesarchiv-bw.de/ofs21/olf/struktur.php?bestand=6101&klassi=001&anzeigeKlassi=001.002). Contact them for a reproduction of Mr Naphtali’s entry.