opennurbs is only a toolkit to read/write the 3dm format. When you read a 3dm file using opennurbs, the geometry in the file is read into memory as objects (curves, surfaces, BReps, layer information, etc.). If you are not working with the Rhino program, you will have to code the display of these objects yourself, or use another framework for this.
What I’m saying is, opennurbs has no code to display the geometry.