Ah, yes. It's the book of Clow. The book with Clow-san's magic cards in, that Kero-chan was guarding. Or....he was supposed to be.

[A book of spells. That could be potentially all the more useful in comparison to her cards. Be more versatile. Still, she gives a shrug. She's not sure, doesn't yet know of the connection between her father and Clow the magician just yet.]

No. I'm not sure if he even really knew much about it. He probably just came across it with his work or something. He's an archaeologist so he has a lot of old books from all sorts of countries.