The viva is not a question and answer session or a quiz. It’s a conversation. Your examiners will lead because this is a conversation with purpose, but there’s a place for you to ask questions too.
First, you can ask to clarify things in the flow of conversation. What did they mean? Could they explain? Can they tell you more so that you can consider something?
Second, you can ask their opinion. What did they think? What would they do? How might I do more with this or follow it up?
Both types of question are fine in the viva.
The first are simply necessary: you might simply need a little more from your examiners so that you can respond as best as possible.
The second are fine but come with the smallest of cautions. The viva is not a Q&A or a quiz, and it’s also not an interview. Candidates sometimes remember the interview advice of having one or two questions prepared to ask the “interviewers”.
But the viva is not an interview. By all means, have questions prepared but only ask if you want to know and only ask if the topic is something that you want to talk about.
You can ask for an opinion or advice, but do it carefully, with a topic that you’ve considered and want to explore more.