If people from Dominica are called Dominicans, what are people from Dominican Republic called?
Dominican is correct for both citizens of Dominica and the Dominican Republic. Congolese (NOT Congonese) is correct for citizens of the Republic of Congo and the Democratic Republic of Congo. British is correct for people from the United Kingdom, and that includes people from Northern Ireland (which is not part of Great Britain), and people from the Isle of Man and the Channel Islands (which are not even part of the United Kingdom). That’s the correct answer, and you can check it on any official website of the respective countries, and before you mutter that you don’t accept French (for the two central African countries), go to the websites of their Permanent Missions to the United Nations.