I have very little familiarity with 3d slicer, so maybe this is a dumb question. But i was wondering if there is a way to reverse engineer .obj file to .seg.nnrd. So i can look into original segmentation attached to dicom data.
I think it would help if you described the origin of your data a bit more. Is it DICOM SEG or DICOM RTSTRUCT?
In any case, you won’t be able to recover the original data, but you can convert the surface representation to labelmap. I think it would be useful for you to read this page, it contains basic information about the representations
https://slicer.readthedocs.io/en/latest/user_guide/image_segmentation.html
As I say surface mesh - labelmap conversion is possible. You can find lots of topics about it in the forum so I encourage to do a search first.