Aparentemente, no Management Studio, em Help
> About
, você encontrará o que procura.
EDIT: Então tem esse também:
To check how many days left for your trial version you can check out the folder under the following path<>\Microsoft SQL Server0\Setup Bootstrap\Log... the creation date of the folder would let you know how long you have been using it. Apart from this, i am not aware of any other places in the DB or server that it is maintained.