You are not expected to have decided upon a research topic when you apply to do honours. Neither are you expected to have a supervisor. Topics and supervisors are decided during the two day honours orientation which is held in the week before semester one begins. (You will be notified the dates if you are offered a place and have successfully enrolled.)
During the orientation workshops there are presentations by researchers from across all areas of the school. These presentations outline current research themes and interests, and available supervisors. Honours students ask questions and you decide what areas you want to work on, and with who. Some of these come with ready made research questions, in other cases you will develop the question in the first two or three weeks of semester with your supervisor.