Which of the Symantec Version you are running on your site?
Have you a Symantec Endpoint Server installed?
If you have a SEPM Server in your Site then login the Console with your Console Admin Access ID.
Go to Admin -> License(There you can find the detail of Expiry)
From Client System you can go the below path
For Window 7 and 8 (SEP.SLF)
C:\ProgramData\Symantec\Symantec Endpoint Protection\12.1.xxxx.xxxx\Data\Config
For Window XP
C:\Documents and Settings\All Users\Application data\Symantec\Symantec Endpoint Protection\12.1.xxxx.xxxx\Data\Config
For more knowledge you can go with attach article
https://www-secure.symantec.com/connect/articles/sep-121-and-license-concept