public RowCursor Search( 
   QueryFilter queryFilter
)

{
  if (!featSceneLayer.HasAssociatedFeatureService)
    return;//Search and Select not supported

  //Multipatch (Object3D) or point?
  //var is3dObject = ((ISceneLayerInfo)featSceneLayer).SceneServiceLayerType 
  //                                  == esriSceneServiceLayerType.Object3D;
  var is3dObject = featSceneLayer.FeatureSceneLayerType == FeatureSceneLayerType.Object3D;
  // Note: call within QueuedTask.Run()
  {
    var queryFilter = new QueryFilter
    {
      WhereClause = "Name = 'Ponderosa Pine'",
      SubFields = "*"
    };

    int rowCount = 0;
    //or select... var select = featSceneLayer.Select(queryFilter)
    using (RowCursor rowCursor = featSceneLayer.Search(queryFilter))
    {
      while (rowCursor.MoveNext())
      {
        using (var feature = rowCursor.Current as Feature)
        {
          oid = feature.GetObjectID();
          var shape = feature.GetShape();
          var attrib = feature["Name"];
          if (is3dObject)
          {
            //shape is a multipatch
          }
          else
          {
            //shape is a point
          }
          rowCount += 1;
        }
      }
    }
  }
}

// Note: call within QueuedTask.Run()
{
  if (!featSceneLayer.HasAssociatedFeatureService)
    return;//no search or select

  //Select all features within the current map view
  var sz = MapView.Active.GetViewSize();
  var map_pt1 = MapView.Active.ClientToMap(new System.Windows.Point(0, sz.Height));
  var map_pt2 = MapView.Active.ClientToMap(new System.Windows.Point(sz.Width, 0));

  //Convert to an envelope
  var temp_env = EnvelopeBuilderEx.CreateEnvelope(map_pt1, map_pt2, MapView.Active.Map.SpatialReference);

  //Project if needed to the layer spatial ref
  SpatialReference sr = null;
  using (var fc = featSceneLayer.GetFeatureClass())
  using (var fdef = fc.GetDefinition())
    sr = fdef.GetSpatialReference();

  var env = GeometryEngine.Instance.Project(temp_env, sr) as Envelope;

  //Set up a query filter
  var sf = new SpatialQueryFilter()
  {
    FilterGeometry = env,
    SpatialRelationship = SpatialRelationship.Intersects,
    SubFields = "*"
  };

  //Select against the feature service
  var select = featSceneLayer.Select(sf);
  if (select.GetCount() > 0)
  {
    //enumerate over the selected features
    using (var rc = select.Search())
    {
      while (rc.MoveNext())
      {
        using (var feature = rc.Current as Feature)
        {
          oid = feature.GetObjectID();
          //etc.
        }
      }
    }
  }
  MapView.Active.Map.ClearSelection();
}