Can Siri turn the page of an e-book I am reading?

You can use Voice Control. Navigate to Settings > Accessibility > Voice Control and toggle on Voice Control. In the eBook app with a book open say, “Swipe left” to turn the page. Say, “Swipe right” to turn the page back. If you prefer a custom phrase such as “Turn the page” you can create a custom command.

Give it a try and see. When you want to turn a page in the book, simply say "Hey Siri, turn to the next page." If the page turns, Siri can do it. If it doesn't Siri, can't. And it would most assuredly be up to whether Siri control has been integrated into the app the book is contained in. That would be up to the App Developer of the app. For example, a user recently asked if Siri could turn the page in a book from Amazon. Siri has not been built into the Amazon App. But Alexa could do it within the Amazon app.

There is no Siri integration with those apps on iPad.