Helix - click coordinates on object inside HelixViewport3D

Question

I would like to know the coordinates of the point in the HelixViewport3D where I clicking.

My task is:
1) RectangleVisual3D as some surface.
2) Clicking on this surface adding 3d-object under mouse pointer.

I found =>this<=, but could not develop the idea further.

Thanks for help :)