From Amazon
Open the book's Amazon page and copy the full address from your browser's address bar — or tap Share → Copy Link on mobile. Author page links work too.
https://www.amazon.com/dp/0439708184
From Apple Books
Open the book in Apple Books, tap Share → Copy Link — or copy the address bar URL if you're using Apple Books on the web.
https://books.apple.com/us/book/id1234567890