public CIMSymbol Symbol {get; set;}

{
  //Note: Must be on QueuedTask.Run

  //Build geometry
  List<Coordinate2D> plCoords = new List<Coordinate2D>();
  plCoords.Add(new Coordinate2D(1, 8.5));
  plCoords.Add(new Coordinate2D(1.66, 9));
  plCoords.Add(new Coordinate2D(2.33, 8.1));
  plCoords.Add(new Coordinate2D(3, 8.5));
  Polyline linePl = PolylineBuilderEx.CreatePolyline(plCoords);

  //Reference a line symbol in a style
  var ProjectStyles = Project.Current.GetItems<StyleProjectItem>();
  StyleProjectItem style = ProjectStyles.First(x => x.Name == "ArcGIS 2D");
  var symStyle = style.SearchSymbols(StyleItemType.LineSymbol, "Line with 2 Markers")[0];
  CIMLineSymbol lineSym = symStyle.Symbol as CIMLineSymbol;
  lineSym.SetSize(20);

  //Set symbology, create and add element to layout
  //CIMLineSymbol lineSym = SymbolFactory.Instance.ConstructLineSymbol(ColorFactory.Instance.BlueRGB, 4.0, SimpleLineStyle.Solid);
  ElementFactory.Instance.CreateGraphicElement(
    layout, linePl, lineSym, "New Line");
}

{
  //Note: Must be on QueuedTask.Run(() => { ...

  //Build geometry
  Coordinate2D coord2D = new Coordinate2D(2.0, 10.0);

  //Reference a point symbol in a style
  StyleProjectItem stylePrjItm = Project.Current.GetItems<StyleProjectItem>()
            .FirstOrDefault(item => item.Name == "ArcGIS 2D");
  SymbolStyleItem symStyleItm = stylePrjItm.SearchSymbols(
                        StyleItemType.PointSymbol, "City Hall")[0];
  CIMPointSymbol pointSym = symStyleItm.Symbol as CIMPointSymbol;
  pointSym.SetSize(50);

  var elemInfo = new ElementInfo()
  {
    CustomProperties = new List<CIMStringMap>() {
    new CIMStringMap() { Key = "Key1", Value = "Value1"},
    new CIMStringMap() { Key = "Key2", Value = "Value2"}
  },
    Anchor = Anchor.TopRightCorner,
    Rotation = 45.0
  };

  var graphic = GraphicFactory.Instance.CreateSimpleGraphic(
                                coord2D.ToMapPoint(), pointSym);

  ElementFactory.Instance.CreateGraphicElement(
    layout, graphic, "New Point", true, elemInfo);
}

{
    //Note: call within QueuedTask.Run()
    CIMSymbol symbolForSwatch = SymbolFactory.Instance.ConstructPointSymbol(ColorFactory.Instance.GreenRGB, 1.0, SimpleMarkerStyle.Circle);
    //You can generate a swatch for a text symbols also.
    var si = new SymbolStyleItem()
    {
        Symbol = symbolForSwatch,
        PatchHeight = 64,
        PatchWidth = 64
    };
}

{
    //Note: Needs QueuedTask to run
    //Get simple renderer from the feature layer
    CIMSimpleRenderer currentRenderer = featureLayer.GetRenderer() as CIMSimpleRenderer;
    if (currentRenderer == null)
        return;
    //Get symbol from the SymbolStyleItem
    CIMSymbol symbolToApply = symbolStyleItem.Symbol;

    //Set symbol's real world setting to be the same as that of the feature layer
    symbolToApply.SetRealWorldUnits(featureLayer.UsesRealWorldSymbolSizes);

    //Update the symbol of the current simple renderer
    currentRenderer.Symbol = symbolToApply.MakeSymbolReference();
    //Update the feature layer renderer
    featureLayer.SetRenderer(currentRenderer);
}

{
      //Get the ArcGIS 2D System style from the Project
      var arcGIS2DStyle =
Project.Current.GetItems<StyleProjectItem>().FirstOrDefault(s => s.Name == "ArcGIS 2D");

      //Note: Needs QueuedTask to run
      //Search for the symbolName style items within the ArcGIS 2D style project item.
      var items = arcGIS2DStyle.SearchSymbols(StyleItemType.PointSymbol, "Circle 1");

      //Gets the CIMSymbol
      CIMSymbol symbolToUse = items.FirstOrDefault().Symbol;

      //Get the renderer of the point feature layer
      CIMSimpleRenderer renderer = featureLayer.GetRenderer() as CIMSimpleRenderer;

      //Set symbol's real world setting to be the same as that of the feature layer
      symbolToUse.SetRealWorldUnits(featureLayer.UsesRealWorldSymbolSizes);

      //Apply the symbol to the feature layer's current renderer
      renderer.Symbol = symbolToUse.MakeSymbolReference();

      //Apply the renderer to the feature layer
      featureLayer.SetRenderer(renderer);
  }