public MapPoint ClientToMap( 
   Point clientPoint
)

internal class GetMapCoordinates : MapTool
{
  protected override void OnToolMouseDown(MapViewMouseButtonEventArgs e)
  {
    if (e.ChangedButton == System.Windows.Input.MouseButton.Left)
      e.Handled = true; //Handle the event args to get the call to the corresponding async method
  }

  protected override Task HandleMouseDownAsync(MapViewMouseButtonEventArgs e)
  {
    return QueuedTask.Run(() =>
    {
      var pointSymbol = SymbolFactory.Instance.ConstructPointSymbol(ColorFactory.Instance.BlackRGB, 8);
      var layout = Project.Current.GetItems<LayoutProjectItem>().FirstOrDefault().GetLayout();
      
      //Convert the clicked point in client coordinates to the corresponding map coordinates.
      var mapPoint = MapView.Active.ClientToMap(e.ClientPoint);
      ArcGIS.Desktop.Framework.Dialogs.MessageBox.Show(string.Format("X: {0} Y: {1} Z: {2}",
          mapPoint.X, mapPoint.Y, mapPoint.Z), "Map Coordinates");
      //Get the corresponding layout point
      var mapFrame = layout.FindElement("New Map Frame") as MapFrame;
      var pointOnLayoutFrame = mapFrame.MapToPage(mapPoint);

      //Create a point graphic on the Layout.
      var cimGraphicElement = new CIMPointGraphic
      {
        Location = pointOnLayoutFrame,
        Symbol = pointSymbol.MakeSymbolReference()
      };
      //Or use GraphicFactory
      var cimGraphicElement2 = GraphicFactory.Instance.CreateSimpleGraphic(
              pointOnLayoutFrame, pointSymbol);

      //At 2.x - LayoutElementFactory.Instance.CreateGraphicElement(layout, cimGraphicElement);

      ElementFactory.Instance.CreateGraphicElement(layout, cimGraphicElement);
      ElementFactory.Instance.CreateGraphicElement(layout, cimGraphicElement2);

    });
    
  }
}

internal class GetMapCoordinates : MapTool
{
  protected override void OnToolMouseDown(MapViewMouseButtonEventArgs e)
  {
    if (e.ChangedButton == System.Windows.Input.MouseButton.Left)
      e.Handled = true; //Handle the event args to get the call to the corresponding async method
  }

  protected override Task HandleMouseDownAsync(MapViewMouseButtonEventArgs e)
  {
    return QueuedTask.Run(() =>
    {
      //Convert the clicked point in client coordinates to the corresponding map coordinates.
      var mapPoint = MapView.Active.ClientToMap(e.ClientPoint);
      ArcGIS.Desktop.Framework.Dialogs.MessageBox.Show(string.Format("X: {0} Y: {1} Z: {2}",
                  mapPoint.X, mapPoint.Y, mapPoint.Z), "Map Coordinates");
    });
  }
}

//var featSceneLayer = ...;
//var sname = featSceneLayer.Name;
await QueuedTask.Run(() =>
{
  if (!featSceneLayer.HasAssociatedFeatureService)
    return;//no search or select

  //Select all features within the current map view
  var sz = MapView.Active.GetViewSize();
  var map_pt1 = MapView.Active.ClientToMap(new System.Windows.Point(0, sz.Height));
  var map_pt2 = MapView.Active.ClientToMap(new System.Windows.Point(sz.Width, 0));

  //Convert to an envelope
  var temp_env = EnvelopeBuilderEx.CreateEnvelope(map_pt1, map_pt2, MapView.Active.Map.SpatialReference);

  //Project if needed to the layer spatial ref
  SpatialReference sr = null;
  using (var fc = featSceneLayer.GetFeatureClass())
  using (var fdef = fc.GetDefinition())
    sr = fdef.GetSpatialReference();

  var env = GeometryEngine.Instance.Project(temp_env, sr) as Envelope;

  //Set up a query filter
  var sf = new SpatialQueryFilter()
  {
    FilterGeometry = env,
    SpatialRelationship = SpatialRelationship.Intersects,
    SubFields = "*"
  };

  //Select against the feature service
  var select = featSceneLayer.Select(sf);
  if (select.GetCount() > 0)
  {
    //enumerate over the selected features
    using (var rc = select.Search())
    {
      while (rc.MoveNext())
      {
        using (var feature = rc.Current as Feature)
        {
          var oid = feature.GetObjectID();
          //etc.
        }
      }
    }
  }

  MapView.Active.Map.ClearSelection();

});