AFAIK, that information is not available via the API.
You can get a list of the resources followed by the authenticated user via the Following API, but that does not work for any other users (I assume due to privacy issues).
You could fetch it the info you are looking for from the database via SQL statements, but that is not officially supported, as the databases could/will change with every product update. In the IBM Connections Forum at developerworks, there is an example for Communities.