Are you referring to a vizinfo panel? There is no built-in way to do this. I'm not sure if the viz.pick command will work with objects added to viz.ORTHO, like the panel. I'll check and update here if there is a way. It maybe necessary to calculate if a mouse click is within a panel's bounds. You could try the following:
1) Calculate the panel bounds using the
node.getBoundingBox method.
2) Handle the mouse down event and determine if the
mouse position is inside the panel bounds.
3) Enable an update function that sets the panel position every frame based on the mouse position. The panel position takes screen coordinates and you can get the mouse position in screen coordinates.
4) Disable the update function when the mouse up event occurs.