Any ideas for retrieving iPhone Siri questions?

There is nothing to retrieve.

Apple balances user privacy against providing services.

They don’t generally have any user identifiable logs for maps, Siri, etc.

read this to understand:

https://www.apple.com/privacy/docs/Differential_Privacy_Overview.pdf

ReneeLav wrote:

Could it really be true I cannot see all of the questions my children have asked Siri over the years?!!! That log would be priceless. Any ideas for retrieving?

That log—which does not exist—would be absolutely priceless data for abusive parents and abusive domestic partners, and for oppressive political regimes, too.

It would also be an invasion of their privacy, and if the feature was available it could be used for stalking and other nefarious purposes. Apple does not keep questions that have been asked of Siri, which makes it impossible for you to see them.