Short answers, pulled from the story.
General Alfred Jodl signed the first Instrument of Surrender in Reims on the 7th of May 1945. He acted as a representative for the Oberkommando der Wehrmacht under instructions from Admiral Karl Dönitz.
The definitive Act of Military Surrender was back-dated to midnight on the 8th of May 1945 but physically signed near 01:00 am on the 9th of May Central European Time. Field Marshal Wilhelm Keitel and Admiral Hans-Georg von Friedeburg signed this document before Marshal Georgy Zhukov in Berlin-Karlshorst.
Western Allies celebrated Victory in Europe Day on the 8th of May because the ceasefire took effect at 23:01 CET on that date. The Soviet Union celebrated Victory Day on the 9th of May 1945 since the signing occurred after midnight Moscow time which was already the 9th of May.
Former Nazi members including Karl Dönitz were taken into captivity as prisoners of war on the 23rd of May 1945. The Allied Powers never recognized the Flensburg Government as validly exercising civil power or representing the state.
The first Instrument of Surrender ceremony took place in a red brick schoolhouse serving as SHAEF headquarters in Reims. This building is now known as the Museum of the Second World War.