Assuming the VMDK files are living in the same directory, one way would be to get the properties of the VM up, then check the properties of the Virtual Disk and see if the Disk File path corresponds to the expected location...
Alternatively, from the Service Console, do a "ps ax | grep VMNAME" (e.g. ps ax | grep PROD-DB) - this will show you the instance for the Virtual Machine you're looking for and will show the full path to which VMX file it's registered from..
