I am an american looking for a dual citizenship. I was born in America, but lived a year in Germany when I was 5, and have just spent another year there through a full scholarship program PPP Congress-Bundestag... I am half German from my mother's side, (she's full German), her parents came to America after the war. Both of my grandparents were German citizens born in Germany. I wish to go to Germany and work for a semester... is this possible with a UN citizen?

If your mother is German, you are German by birth as well.
You could contact the nearest German Consulate/Embassy for details and information.