protected virtual void OnToolMouseDown( 
   MapViewMouseButtonEventArgs args
)

public ProSnippetMapTool()
{
  //Set the MapTool base class' OverlayControlID to the DAML id of your embeddable control in the constructor
  this.OverlayControlID = "ProAppModule1_EmbeddableControl1";
}

protected override void OnToolMouseDown(MapViewMouseButtonEventArgs e)
{
  if (e.ChangedButton == System.Windows.Input.MouseButton.Left)
    e.Handled = true;
}

protected override Task HandleMouseDownAsync(MapViewMouseButtonEventArgs e)
{
  return QueuedTask.Run(() =>
  {
    //assign the screen coordinate clicked point to the MapTool base class' OverlayControlLocation property.
    this.OverlayControlPositionRatio = e.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");
    });
  }
}