How can I quickly find any WIM files that are mounted using the Deployment Image Servicing and Management (DISM) tool?

A. DISM has a great /get-mountedwiminfo option that gives basic information about any mounted WIM, including the folder the WIM is mounted at and if it's writable. This is all the info you need to dismount it.

C:>dism /get-mountedwiminfo

 Deployment Image Servicing and Management tool
 Version: 6.1.7600.16385

 Mounted images:

 Mount Dir : d:Tempmount1
 Image File : d:OS ImagesWindows 7 Ult 64-bitsourcesinstall.wim
 Image Index : 4
 Mounted Read/Write : Yes
 Status : Ok

 The operation completed successfully.