The workspaces are stored locally in the FME Server System Share's 'repositories' folder, e.g. C:\\ProgramData\\Safe Software\\FME Server\\repositories\\Samples\\austinApartments
You could use the Directory and File Pathnames Reader in combination with the FME Workspace Reader on these System Share folders to get similar kinds of information about each workspace.
Alternatively, the FME Server REST API repositories endpoints could also programmatically search the published workspaces. Use this with the HTTPCaller or another API application, with JSON transformers to parse the returned results.
Hope that helps!