public sealed class FeatureSceneLayer : CompositeLayer, ArcGIS.Desktop.Core.IMetadataInfo, ILayerContainer, IMetadataSource, ITableDefinitionQueries, System.ComponentModel.INotifyPropertyChanged  

{
  // Note: call within QueuedTask.Run()
  {
    //Create with initial visibility set to false. Add to current scene
    var createparams = new LayerCreationParams(new Uri(sceneLayerUrl, UriKind.Absolute))
    {
      IsVisible = false
    };

    //cast to specific type of scene layer being created - in this case FeatureSceneLayer
    var sceneLayer = LayerFactory.Instance.CreateLayer<Layer>(
             createparams, MapView.Active.Map) as FeatureSceneLayer;
    //or...specify the cast directly
    var sceneLayer2 = LayerFactory.Instance.CreateLayer<FeatureSceneLayer>(
             createparams, MapView.Active.Map);
    //ditto for BuildingSceneLayer, PointCloudSceneLayer, IntegratedMeshSceneLayer
    //...
  }
}

{
  featSceneLayer = MapView.Active.Map.GetLayersAsFlattenedList()
                   .OfType<FeatureSceneLayer>().FirstOrDefault();
  var scenelayerName = featSceneLayer?.Name;
}

{
  var sname = featSceneLayer.Name;

  // Note: call within QueuedTask.Run()
  {
    //Select all features within the current map view
    var sz = MapView.Active.GetViewSize();

    var c_ll = new Coordinate2D(0, 0);
    var c_ur = new Coordinate2D(sz.Width, sz.Height);
    //Use screen coordinates for 3D selection on MapView
    var env = EnvelopeBuilderEx.CreateEnvelope(c_ll, c_ur);

    //HasAssociatedFeatureService does not matter for SelectFeaturesEx
    //or GetFeaturesEx
    var result = MapView.Active.SelectFeaturesEx(env);
    //var result = MapView.Active.GetFeaturesEx(env);

    //The list of object ids from SelectFeaturesEx
    var oids1 = result.ToDictionary().Where(kvp => kvp.Key.Name == sname).First().Value;
    //TODO - use the object ids

    MapView.Active.Map.ClearSelection();
  }
}