If you've previously disabled CIFS oplocks for a specific volume or qtree, and now you want to reenable them, you can do so by using the qtree oplocks command.
sys1> options cifs.oplocks.enable on sys1> qtree oplocks /vol/vol2/proj enable
You can verify the update by using the qtree status command, using the name of the containing volume if you updated the CIFS oplocks for a qtree.