public ValueTuple<bool,bool> HasSymbolLayerDrawingAdded()

{
    //SLD can be added to feature layers and group layers
    //For a group layer, SLD controls all child feature layers
    //that are participating in the SLD

    //var featLayer = ...;//retrieve the feature layer
    //var groupLayer = ...;//retrieve the group layer
    //Check if the layer has SLD added -returns a tuple
    //Note: Run within a QueuedTask
    var tuple = featureLayer.HasSymbolLayerDrawingAdded();
    if (tuple.addedOnLayer)
    {
        //SLD is added on the layer
    }
    else if (tuple.addedOnParent)
    {
        //SLD is added on the parent (group layer) - 
        //check parent...this can be recursive
        var parentLayer = GetParentLayerWithSLD(featureLayer.Parent as GroupLayer);

        //Recursively get the parent with SLD
        GroupLayer GetParentLayerWithSLD(GroupLayer groupLayer)
        {
            if (groupLayer == null)
                return null;
            //Must be on QueuedTask
            var sld_added = groupLayer.HasSymbolLayerDrawingAdded();
            if (sld_added.addedOnLayer)
                return groupLayer;
            else if (sld_added.addedOnParent)
                return GetParentLayerWithSLD(groupLayer.Parent as GroupLayer);
            return null;
        }
    }
}

{
    //A layer may have SLD added but is not using it
    //HasSymbolLayerDrawingAdded returns a tuple - to check
    //the layer has SLD (not its parent) check addedOnLayer
    if (featureLayer.HasSymbolLayerDrawingAdded().addedOnLayer)
    {
        //the layer has SLD but is the layer currently using it?
        //GetUseSymbolLayerDrawing returns a tuple - useOnLayer for 
        //the layer (and useOnParent for the parent layer)
        if (!featureLayer.GetUseSymbolLayerDrawing().useOnLayer)
        {
            //enable it
            featureLayer.SetUseSymbolLayerDrawing(true);
        }
    }

    //Enable/Disable SLD on a layer parent
    if (featureLayer.HasSymbolLayerDrawingAdded().addedOnParent)
    {
        //check parent...this can be recursive
        var parent = GetParentLayerWithSLD(featureLayer.Parent as GroupLayer);
        if (parent.GetUseSymbolLayerDrawing().useOnLayer)
            parent.SetUseSymbolLayerDrawing(true);
    }

    //Recursively get the parent with SLD
    GroupLayer GetParentLayerWithSLD(GroupLayer groupLayer)
    {
        if (groupLayer == null)
            return null;
        //Must be on QueuedTask
        var sld_added = groupLayer.HasSymbolLayerDrawingAdded();
        if (sld_added.addedOnLayer)
            return groupLayer;
        else if (sld_added.addedOnParent)
            return GetParentLayerWithSLD(groupLayer.Parent as GroupLayer);
        return null;
    }
}