The REST API documents that for a bpm/caseVariable GET request, you need the case_id and the variable_id. I can find the case_id from bpm/case GET but where does the variable_id come from? I haven't seen it returned in any of the REST API that I've used to date.
It would be really helpful if the JSON structure for each of the calls was listed in the documentation.
In order to get all variables of a given case take a look here http://documentation.bonitasoft.com/web-rest-api-examples (get process instance data values)
Bonitasoft empowers development teams with Bonita, the open-source and extensible platform to solve the most demanding process automation use cases. The Bonita platform accelerates delivery of complex applications with clear separation between capabilities for visual programming and for coding. Bonita integrates with existing solutions, orchestrates heterogeneous systems, and provides deep visibility into processes across the organization.