Welcome to AAPK. Most, if not all the information about them is stamped on the knife itself. You know the manufacturer and pattern number (what you’ve called the serial number) from the stamps on each knife. On Case knives you can also determine when they were made as there is a date code system. All of the information needed is explained here by clicking on Research in the header at the top of this page, and following the prompts.
The other thing many want to know is “how much is it worth? The best source of value is to do an advanced search on eBay for sold listings of the same or similar knives. Once you know the maker, the pattern number, and the manufacturing date, just put that into eBay’s search, and see what is found.
Have fun with your research.
I hope you find learning about your grandfathers knives to be interesting and enjoyable. You’re fortunate to have something he valued.