I have graphics card with two monitors connected, and extended desktop on second monitor.
Here is info how to use second display with rhino.
Oficially rhino not support multidisplay configuration. You need to:
1. Create new viewport by clicking View-Viewport layout - new viewport.
2. Make it floating by choosing View - Viewport layout - Float viewport
3. Bring floating viewport window to second display, then expand it.
Now you can check what you doing from different point of view. I using it to ensure what point snapped with osnap turned on, when points one above another.
Keep in mind that on the next load your saved file this new viewport will back on the first display and float will be turned off. You need to choose it, turn on float again, then bring it back.