Launch Powershell from DDC Studio, or from powershell: asnp Citrix*
Get-BrokerCatalog -Name Nameofyourcatalog
Copy the ProvisioningschemeID and paste into notepad
Get-ProvScheme -ProvisioningSchemeUid ProvisioningschemeIDcopiedfromnotepad
Find MasterImageVM in the output. This is the associated master image