The VMClassId is formed like this "2!9;PersonSeeker" - 2!9 is the externalid for the rooted object ($null$ if null), followed by a semicolon and the name of the ViewModel or a Nesting within a ViewModel.

You can see the JSon data of a Turnkey page by appending/debugging to the URL. In this data, you will find your current VMClassIds.

See also: The_ExternalId_explained