Hello, Gabriel.
We also didn't find a standard solution for this yet, but as a workaround to know the approvers which took decisions in a request workflow, we query two tables:
1. In GRFNMWRTINST we get the INSTANCE_ID of the request by putting its number in the EXTERNAL_KEY_DIS field.
2. Filtering GRFNMWRTDATLG with this INSTANCE_ID, you will have a list of the request paths and the decisions already taken in each of them, together with the responsibles.
Although notthe best solution,I hope it helps.
Regards,
Marcelo Monsores