Around 40,000 individuals were expatriated by the Nazis on an individual basis between 1933 and 1945. The names of these individuals were published in Ausbürgerungslisten (Expatriation Lists). There is a 3-volume compilation of all of these lists, along with an index according to name and place of birth, that was published in the 1980s, edited by Michael Hepp. You can find it here; an ebook is available through many university library programmes, and it may also be in a library in your area. Note that it does not mean that your ancestor was not stripped of their citizenship if their name does not appear here; of the approximately 300,000 individuals who had their citizenship formally stripped during National Socialism, only a fraction were denaturalised through this provision.

After the Second World War, many parts of Germany became Polish or Czech territory, such as Königsberg (Kaliningrad), Breslau, or other cities. Many of the birth, marriage, and death certificates from these areas are now held in the Landesarchiv Berlin; you can see which holdings Berlin possesses by looking here.