Are you referring to the query link in the SEP Content Distribution Monitor?
Schema reference guides for SEP 11 and 12.1:
http://www.symantec.com/docs/TECH102544
http://www.symantec.com/docs/DOC4324
As a simple example, here is SQL code to retrieve the size of the stored content in the database (without client packages) in GB:
SELECT SUM(DATALENGTH(CONTENT))/1024.0/1024/1024
AS "content size in GB" FROM BINARY_FILE
WHERE TYPE='DownloadedContentFile'
Should work with embedded and SQL Server database.