Being a philosophy grad I have a bit of a head start with medical ethics/bioethics. I'm going to go back through all my old reading material and dig out some cases - I'll try and do summaries for them and post them on here. I think the main thing is not to try and formulate responses to specific cases in the hope that they come up but become familiar with how to reason around ethical dilemmas. I believe at interview they're looking for your thought processes as opposed to coming to a conclusion and making a decision, although I could be wrong.
With ethical cases the main thing I'd advise is to remain as objective as possible - try not to let any emotional bias' creep through your reasoning process. The 'should paedophiles be castrated' case is a classic one to try and trap people out. Most people react extremely passionately to anything related to paedophilia so struggle to remain objective and discuss it without getting muddied. Particular to medicine, if you reason about the cases from the perspective of a doctor, then you'd need to show you're thinking about things that are important in a physicians ethical reasoning i.e. consent. You could ask the question as to whether in this case, paedophiles would be forced to be castrated, or are presented with the option to be - which changes the dilemma significantly.
If there's a current case I'd prep for that I think is likely to make an appearance, it's the Charlie Gard case. With that you need to be thinking about how to determine what's in the best interests of a patient that can't communicate - and in particular for children, how to navigate complex medical cases with their parents, who are almost as much the patients as the child is. What's unique with the Gard case is how it became politicised, and the patient almost got lost behind a legal/political campaign that sprung up around him.