Concrete planning about the use of the atomic bombs was not really made until very late in the game when the bombs became military realities. As a result there was never any serious thought that they would be used against Germany.

President Roosevelt apparently asked General Groves, head of the Manhattan Project, in December 1944 whether they could be ready to use one against Germany soon, but it was dismissed out of hand for timing and logistical reasons.

Entirely separately, Werner Heisenberg was once asked by an aide of Göring's about a rumor that Dresden would be atomic bombed, in the summer of 1944. Heisenberg thought it was a ridiculous notion and dismissed it. I've wondered (see the previous link) where that strange question might have come from, and whether it had some basis in a botched counter-intelligence move on behalf of Groves.

But no even preliminary list of German cities was ever created in the United States. Even the provisional list of Japanese cities was not created until May 1945, a week after the formal German surrender.