It was around 2010 when I watched it but translated cartoons was arriving kinda late to my country (Poland) so keep that in mind. I'm not sure if it was the main plot of the cartoon but they were collecting some kind of gems and puting them in sockets located in the book cover. And when they put all gems in sockets a final socket in the middle of the cover opened.
1 Answer
Magi-Nation?
The wiki explains Dreamstones:
The Dreamstones were twelve stones hidden all over the Moonlands and act as keys to unlocking the Core Glyph from the Book of Elders. One Dreamstone was designated to each of the Moonlands. Originally, only eleven were thought to exist, but a twelfth slot was revealed for the Core when the initial eleven were put into the Book of Elders.