How to add Active Directory Schema Snap-in on Windows Server 2008 R2?
Click 'Start' -> 'Run'. Input 'cmd' and click 'OK'. Run the following command
Regsvr32 Schmmgmt.dll
Click Start -> Run. Input mmc and click OK.
On the File menu, click Add/Remove Snap-in, click Add, and then click Active Directory Schema. Click Add, click Close, and then click OK.
On the File menu, click Save As, choose destination path and type the console name, then click Save.