It is important to note that EA Sports has discontinued official support for Tiger Woods PGA Tour 08. The master servers for online multiplayer are offline, meaning a CD key will only grant you access to the local career mode and offline tournament play.

If you are looking for the CD key (serial number) for Tiger Woods PGA Tour 08

HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Electronic Arts\EA Sports\Tiger Woods 2008\ergc 32-bit Systems