I think there is no “ready-to-use” infrastructure for this, but you can:
- Use a callback to observe the mouse clicks in the 3d view (see https://github.com/Slicer/Slicer/blob/master/Modules/Loadable/Segmentations/Widgets/qMRMLSegmentEditorWidget.cxx#L2565);
- when you process the events, you get the model display manager from the view ;
- you get the mouse event position from the interactor;
- you call the display manager Pick method (this will return the cellID, the modelNodeId and the RAS coordinates of the picking).
Another option, it would also to write a custom model display manager, or you can have a look at Select cells of a 3D model (where you can use the crosshair or a markup point, which involves much less coding).