We need to know which country where you claim citizenship. It is also important for the purposes of forms and relevant evidence that we understand if you are a dual citizen.
What should I put for my primary country of citizenship?
This is the country whose passport you have used to enter the USA. If you didnt have a passport while entering this is the country that you have indicated as your citizenship in USCIS/DHS documents. If you are unsure, you could look at your I-94 to ascertain what is your primary country of citizenship,
Secondary country of citizenship:
If you are a dual citizen, please list your second country of citizenship. You should include this information even if you don't currently have a passport from this country. Unless you have successfully surrendered your citizenship, you should always include this information.