Which Geneva Convention Protocol? As far as the Geneva and Hauge Conventions go, the things that would have been a counter would have been article XIV in the Hague Convention, but bombing had been already a common thing.

As for the Geneva Conventions, Nazi Germany by the time of the Dresden bombings already essentially disbanded and discarded the Geneva Convention Protocols with the absolutely hideous treatment of prisoners. In terms of the Poisonous Gases and Biochemical Weapons part of the convention, I'd wager retaliation would have been a very tangible reason to avoid using such weapons.

The problem with this question is that it assumes that Nazi Germany was faultless and that the Dresden Bombings weren't preceded by many egregiously inhumane actions of Nazi Germany.

That said, by the time Dresden was bombed, the Nazis already discarded most of the pretense of treating their prisoners humanely (vis a vis the Geneva Convention) so although they did not officially suspend it, to say they didn't ignore it would be a grave misrepresentation.

Furthermore, by the time Dresden was bombed, the Nazis were already at the cusp of defeat.

3.3 million of the 5.5 million Soviet POWs (60%) captured by the Germans died in German captivity so it wasn't as if they were abiding by any convention. Most of them were just herded together out in the open behind barbed wire and left to die of starvation and exposure. Two million died that way in the first six months of the war. Tens of thousands, maybe hundreds of thousands, were outright executed. Many thousands were gassed in Auschwitz. The rest died slower deaths through gradual starvation, overwork, and diseases caused by appalling overcrowding and sanitary conditions.

By comparison: the Germans captured 232,000 American and British soldiers of which 8,350 died (3.5%). The Soviets captured 3 million German prisoners of war of which 400,000 died (13%).

Streit, Christian. "Soviet Prisoners of War in the Hands of the Wehrmacht." War of Extermination: The German Military in World War II, 1941-44, eds. Hannes Heer and Klaus Naumann (2000).

Glantz, David M. Barbarossa: Hitler’s Invasion of Russia, 1941. Stroud, Gloucestershire: Tempus, 2001.

Hilberg, Raul. The destruction of the European Jews. New York: Holmes & Meier, 1985.