Sydney is holding the 'mini-multiple interview' because it has a higher reproducibility rate than the old interview system.
It would be unethical to tell you the kind of questions they ask but if you know why you want to do medicine and feel strongly about it, you should do fine.
In the letter they send you about the interview, it should hint at what they're looking for.
Honestly, what do you want from a doctor? Why do you want to be a doctor?
Do you even know anything about the health care system?
Answering these questions will help you prepare for the interview.
Good luck.