The point returned from ISelectionMgr::GetSelectionPoint2 or ISelectionMgr::IGetSelectionPoint2 cannot lie on the object that was selected. For example, the user can select an edge when the edge is within the pick radius of their mouse cursor. However, to get a point on a face, edge, or vertex, use that object's GetClosestPointOn method.
To do this, get the IFace2, IEdge, or IVertex object using the ISelectionMgr::GetSelectedObject6 method, and then use that object to call GetClosestPointOn. Pass the X,Y,Z values returned from ISelectionMgr::GetSelectionPoint2 or ISelectionMgr::IGetSelectionPoint2, and the GetClosestPointOn method will return the closest X,Y,Z point that is on the face, edge, or vertex.
If the selected object is sketch geometry, then the coordinates returned are in sketch space. The coordinates are 2D and related to the origin of the sketch that owns the selected geometry.