Moving this over to the OptiX sub-forum.
Please read these two recent discussions about potential problems when starting optixTrace with other traversable handles than the root IAS:
https://forums.developer.nvidia.com/t/traverse-a-bvh-from-a-specific-node/262208
https://forums.developer.nvidia.com/t/tracing-non-homogenous-unstructured-volumes/271503/4
What exactly is not working?
You don’t get the correct traversable handle you put into the OptixInstance on the host when calling optixGetInstanceTraversableFromIAS?
What are your OptixTraversableGraphFlags?
You don’t get any intersections? Mind that your ray is in world space coordinates inside the ray generation, closesthit and miss programs.
What the world space is, depends on which traversable handle is used inside optixTrace because that defines the transform list.
If you have specific issues with OWL, please keep discussing these inside the github repository with the original author.