You can’t expect any questions to be easy in the viva. Some could be simple for you to answer, however, but only because of what you know about your research, your discipline and your talent as a researcher.
Possible opening questions could be hard – Can you summarise…? How would you define…? – but they’re also picked deliberately as an opportunity for you to start well. Perhaps you would be talking about something that is simple for you to explain due to your experience.
There’s a common observation about vivas that “the last question will be hard.” I don’t know how true this is in general. Even in cases where a final question is more challenging, it’s probably better to frame this as difficult. Even given your knowledge and talent, questions could be difficult for you to respond to. You can’t expect questions to be easy, and you also can’t expect particular questions in general.
But you can improve confidence and talent through practice. Put yourself in situations where you need to think. Have a mock viva to rehearse for the real one. Meet your supervisor to discuss your research. Go for coffee with friends to see what they want to know about your thesis.
You can’t prepare by practising only particular questions – easy, simple, hard or difficult – but you can get better at responding to questions in general.