"Book" is a homograph. If someone was arresting a novel, he could be said to book the book.
While I do not know the riddle, I'm guessing the homophone involved is air/heir.
plane and plain
"What is a road lined with scales?"
A homophone for bookmark would be "book mark". It's still a homophone even though it is two words. That is the only homophone for bookmark.
caller & collar
"What is the hairy bark of an evergreen?"
The answer to the riddle in the book "Ghost Town at Sundown" is a coffin.
The Harry Potter book with the memories of Tom Riddle in it is The Chamber of Secrets. The diary of Tom Riddle became alive in that book and he was who Harry had to fight.
book
The book was a horcrux of voldemorts and the tom riddle that was in the chamber of secrets was preserved in the book. when harry stabbed the book the horcrux was destroyed and so was the preseved tom.
the book says "receipt"
The Riddle