There’s a simple, foolproof, two-step process for getting lots of potential viva questions:
- Google “PhD viva question list”.
- Take a look at the results.
Not every question you find from these results will be relevant. Some you can discard, some you can refine, some you will see connections that you could make more specific for your research.
Ask your supervisors, ask your friends and colleagues to see what they think. What questions are likely? What might they say? What do they want to ask you and how are they prepared to help you?
The goal is not to prepare an answer for every possible question: that’s an impossible task. Instead get a sense of what can come up. Through exploration you can become certain you are capable of answering questions in the viva.