`gpu_map.json` is expected in the format and can be generated with `condor_status_to_gpu_map.py <path/to/condor_status.json>`, where `condor_status.json` is generated by calling `condor_status -json > condor_status.json` on the cluster:
For getting a debug dump of the class ads at the end of the `endTransaction`, build with `-DVERBOSE` (automatically set for `Debug` or `RelWithDebInfo` builds) and set `SCHEDD_DEBUG=D_FULLDEBUG` in the condor config.