public class CIMGeometricEffectOffset : CIMGeometricEffect, System.ComponentModel.INotifyPropertyChanged, System.Xml.Serialization.IXmlSerializable  

/// <summary>
/// Create a line symbol with a dash and two markers.<br/>          
/// </summary>
/// <remarks>
/// This line symbol comprises three symbol layers listed below: 
/// 1. A solid stroke that has dashes.
/// 1. A circle marker.
/// 1. A square marker.
/// ![LineSymbolTwoMarkers](http://Esri.github.io/arcgis-pro-sdk/images/Symbology/line-dash-two-markers.png)
/// </remarks>
/// <returns></returns>
internal static Task<CIMLineSymbol> CreateLineDashTwoMarkersAync()
{
    return QueuedTask.Run<CIMLineSymbol>(() =>
    {

        var dash2MarkersLine = new CIMLineSymbol();

        var mySymbolLyrs = new CIMSymbolLayer[]
        {
            new CIMSolidStroke()
            {
                Color = ColorFactory.Instance.BlackRGB,
                Enable = true,
                ColorLocked = true,
                CapStyle = LineCapStyle.Round,
                JoinStyle = LineJoinStyle.Round,
                LineStyle3D = Simple3DLineStyle.Strip,
                MiterLimit = 10,
                Width = 1,
                CloseCaps3D = false,
                Effects = new CIMGeometricEffect[]
                {
                    new CIMGeometricEffectDashes()
                    {
                        CustomEndingOffset = 0,
                        DashTemplate = new double[] {20, 10, 20, 10},
                        LineDashEnding = LineDashEnding.HalfPattern,
                        OffsetAlongLine = 0,
                        ControlPointEnding = LineDashEnding.NoConstraint
                    },
                    new CIMGeometricEffectOffset()
                    {
                        Method = GeometricEffectOffsetMethod.Bevelled,
                        Offset = 0,
                        Option = GeometricEffectOffsetOption.Fast
                    }
                },
            },
            CreateCircleMarkerPerSpecs(),
            CreateSquareMarkerPerSpecs()
        };
        dash2MarkersLine.SymbolLayers = mySymbolLyrs;
        return dash2MarkersLine;
    });
}
private static CIMMarker CreateCircleMarkerPerSpecs()
{
    var circleMarker = SymbolFactory.Instance.ConstructMarker(ColorFactory.Instance.BlackRGB, 5, SimpleMarkerStyle.Circle) as CIMVectorMarker;
    //Modifying the marker to align with line
    //First define "markerplacement"
    CIMMarkerPlacementAlongLineSameSize markerPlacement = new CIMMarkerPlacementAlongLineSameSize()
    {
        AngleToLine = true,
        Offset = 0,
        Endings = PlacementEndings.Custom,
        OffsetAlongLine = 15,
        PlacementTemplate = new double[] { 60 }
    };
    //assign the markerplacement to the marker
    circleMarker.MarkerPlacement = markerPlacement;
    return circleMarker;
}
private static CIMMarker CreateSquareMarkerPerSpecs()
{
    var squareMarker = SymbolFactory.Instance.ConstructMarker(ColorFactory.Instance.BlueRGB, 5, SimpleMarkerStyle.Square) as CIMVectorMarker;
    CIMMarkerPlacementAlongLineSameSize markerPlacement2 = new CIMMarkerPlacementAlongLineSameSize()
    {
        AngleToLine = true,
        Endings = PlacementEndings.Custom,
        OffsetAlongLine = 45,
        PlacementTemplate = new double[] { 60 },
    };
    squareMarker.MarkerPlacement = markerPlacement2;
    return squareMarker;
}