How should I write for the oral presentation topic?
You might want to talk about the details of the training that cadet pilots receive in Adelaide. Things such as the number of modules, focus of each module, aircraft flown, total hours you end up with, ground school subjects you study while training, total number of weeks you stay in ADL, the licenses you end up with... basically anything you can find about the training aspects of the CPP.
I remember I went in and pulled my speech out of my backside, so I didn't go very far before I ran out of things to say. Admittedly that was not a good move, so in the remaining time the HR ended up asking me further questions about cadet training. Just prove to them you can speak decent English and you should be okay.