This is a question they ask just to make sure where your money is coming from. You will be presenting to the interviewer a statement on your bank account and other documents, so of course, they know who will be sponsoring your trip.
However, answer simply and clearly. Show proof of all your income and savings if you plan to finance your trip with your own financial means.
On the other side, if someone will be sponsoring your visit to the US then present your relationship with them, their income and other details to prove that they are capable to cover your financial needs during your stay in the US. If you feel the interviewer is giving you space to talk more about the issue, tell him your sponsor’s occupation and other details that will prove to him you have a strong connection, and there is a strong reason why this person is sponsoring your trip.
