Please check the following OOTB activities. They may give you some help.
Activity "pyGetTagCasesAcrossWorkpools" - Instantiates a data page (D_TagCases) containing the cases related to the tag named in the input parameter across all workpools in the current application.
Activity "pyGetUseCasesInAnApplication" - Get Use Cases in an application and built-on applications by calling list view.
Activity "GetUseCaseCount" -
Activity "GetUseCaseMatrix" -
Activity "pxCaseCount" - This activity returns the count of case type rules in the current Application. Call this activity to get the case type count for the currrent application. The case type count is returned in out parameter 'CaseCount'. It uses the current application's configuration to use Built On Application ruleset list.
Today I heared how I can get the information we need. We get the information by using the "Usage Validation Utility". this Utility can be started when logging in as user UVUser@pega.com in the PEGA Designer Studio. After logging in I have to choose a start/end date and select the data I am interested in. Then press the "run report" butten. The result is a zip file with 1 or more csv files with the extracted data.