I really don't even understand what exactly you're asking here. Please try again and explain carefully.
You just add to go on your vCenter Web Client through the Datastore tab , then clic on the datastore you want, then clic on the VM tab and the VM that currently using the datastore appears... or not.
This is the same manipulation to know which host is currently using the datastore if you clic on Host tab.
A little screenshot to explain :