Hi Mel,
In that case it's a C2, but I was confused by the history, probably wrong on airwar where the C2 is shown with the lower wing removed and vice versa!!
http://www.airwar.ru/enc/other1/doc3.html
"The first - Do.C3 took off on September 18, 1931.It was a double all-metal one and a half wing, equipped with a 1225-cylinder Hispano-Suiza 12Y engine with a capacity of 725 hp."
http://www.airwar.ru/enc/other1/doc2.html
"Following him immediately appeared two reconnaissance seaplane. The first - Do.C3 took off on September 18, 1931. The following year, the aircraft was converted into a high-wing - Do.C2 (or Do.C2A). In addition to the new wing, a Hispano-Suiza 12 Nbr engine with 740 hp was installed on it. and an additional fuel tank."
It looks like they've got the designations transposed as why would the C3 precede the C2 ? Should have checked Histaviation but that can be a real pain now! (and I don't mean because of my sodding hand which makes everything a pain)
Just looked at both versions of Histaviation (one totally broken and not listed on the other) Not shown on Luftarchiv and Wiki not much help either, merely redirecting to the Parasol Do.10