FNB's post is a good, pertinent summary of the Panel Interview process for both Cadet and Direct Entry applicants.
Cadet interview questions will be commensurate with experience, although expect questions of a technical nature pertaining to aeroplanes in the Qantas fleet. No one expects you to know the function of the 'THR' button on the 744, but an appropriate knowledge of *basic* heavy jet aerodynamics - winglets, turbofans (versus propellers), Bernoulli etc - would help significantly. Broad questions on geography, route network etc also go without saying...
What you don't need aeronautical experience to do is to know every last detail about Qantas fleet, corporate structure and general history. Questions on these areas are a quick way to eliminate the stragglers. Plenty of applicants out there can fly an aeroplane - you need to differentiate yourself from the pack by showing your enthusiasm and motivation to work for the big Q.
Best of luck.
IORRA