public enum FeatureSceneLayerType : System.Enum, System.IComparable, System.IConvertible, System.IFormattable, System.ISpanFormattable  

//var featSceneLayer = ...;
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;
await 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)
      {
        var oid = feature.GetObjectID();
        var shape = feature.GetShape();
        var attrib = feature["Name"];
        if (is3dObject)
        {
          //shape is a multipatch
        }
        else
        {
          //shape is a point
        }
        rowCount += 1;
      }

    }
  }

});

//var featSceneLayer = ...;
if (featSceneLayer.HasAssociatedFeatureService)
  return;//Search and Select not supported

await QueuedTask.Run(() =>
{
  QueryFilter qf = new QueryFilter()
  {
    ObjectIDs = new List<long>() { 6069, 6070, 6071 },
    SubFields = "*"
  };
  featSceneLayer.Select(qf, SelectionCombinationMethod.New);

  featSceneLayer.HideSelectedFeatures();
  var selectionCount = featSceneLayer.SelectionCount;

  featSceneLayer.ShowHiddenFeatures();
  selectionCount = featSceneLayer.SelectionCount;

});