You could use "pickPoint" in combination with regular 3D snaps, or you can use the "on mousePoint" event in combination with "mapScreenToWorldRay" and some ray casting. The first should be fine if all you need is a 3D world coordinate; the latter is probably better if you need to know which object was clicked.
PS: Looking at the documentation, I realize that maybe the first variant could use the "boxPickNode" function to also find out what object was clicked on...?
Martin B
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