If you have the original ISO or physical media, the key is often pre-staged. During the installation wizard, the "Product Key" field may be auto-populated. If not, look for a file named DefaultSetup.ini in the \x64 folder of the installation media.
The installation is not the end. SQL Server 2012 requires activation . When your server connects to the internet (or via phone), Microsoft’s activation servers check that key. If the key is blacklisted (which all public "i---" keys are), you will see: i--- Sql Server 2012 Enterprise Edition Product Key
Your database holds the most valuable asset of your company: . Is saving a few thousand dollars worth losing everything? If you have the original ISO or physical
, keys for all editions, including Enterprise, are available in the downloads section. Microsoft Learn SQL Server 2012 Enterprise Licensing Models The installation is not the end