That really depends on the university and assessment style. I had such a variety across interviews. The key thing to note is that they wont be assessing you veterinary knowledge. Questions are often focused on an interesting case you saw, your career goals, what you learnt from placements, your personal statement and your understanding of the profession. One thing to note is that MMIs can be really random. I also had to tell someone how to build something. It can be truly random.
I wouldn't say there's specific things to ask for on placement but jsut ask questions when you dont know soemthing and write everything down in a notebook
Id say having a knowledge of current issues in the vet world is a good idea. Maybe see if you can sign up for the vet times