You can't assume anything about the interview. Saying that it is at headquarters isn't helpful because some companies don't have a single HQ.
The person you have been in contact with should be the one to provide the exact time and location.
They should also provide any other relevant information such as: park in the visitor lot, go in the East entrance , and stop by the receptionist on the 2nd floor. They may even have a document to send you that includes a map, GPS coordinates, and nearest subway station.
They may give you alternate numbers to call if you are running late, or if you have any issues on the day of the interview.
I would send a quick email reply:
I look forward to the interview on the xth of January.
What time should I arrive at the interview location so that I can take
care of any entrance procedures, or to complete any paperwork?
I understand it is to be held at your headquarters building, but I
have never been there. Can you please send me the address of the
building and the room number. Is there is any other information such
as parking that I need to know before I arrive?
I look forward to your reply.