"We purchased a PowerEdge T310 some time ago and it came with Server 2008 OS and 10 CALs, where can I find the details of these licenses? I.e what type of license, Open, Select, etc..."
OS license key/COA will be on a sticker on the server. CAL's will have come in a paper format - these must be retained for audit purposes and cannot be replaced (must re-purchase if lost).
"Ans since we purchased it in early 2012, are we entitled to Server 2012 OS and CALs?"
No. The ONLY way you would be entitled to run Server 2012 with your existing license (without having to buy a newer license) is if your server actually shipped from Dell WITH a 2012 license/COA and 2008 R2 was installed using "downgrade rights".