I agree with Utkarsh. Actually, I think it should be .xml. Extensions are relative to the format on disk, not what the data represents. When you export a color map in ParaView, it shows up as a .json, not .paraviewcolormap. The same discussion can be had for cgns files. ParaView (and a lot of other people) write cgns files as .cgns. I think it should be .hdf or .adf, one of the two disk implementations of cgns. That’s the first thing you need to know to select a reader.