Often, this very question gets dodged or answered randomly. You may be lucky if you answer it correctly. There might be cases where the job might be posted on a specific website, and you manage to say that exact name. That's the ultimate blunder. HR would like to hire a candidate who is serious about the position, the one who is dedicated enough to secure a position. It is understandable for you to remember every job you applied for. To rectify that situation, gather this information before sitting for the interview. If you have a person who referred you to this job and they work for the same company, it could be very beneficial for you. In that case, you could say, "I heard about this position from an employee of this company. She is a friend of mine and suggested this opportunity. She spoke highly of this company, which made me interested in being a part of it. " Remember to be as honest and confident as you can.