public DefinitionQuery( 
   string name,
   string whereClause
)

          // Note: Run within QueuedTask.Run
          // Set the spatial filter geometry

          //Get the geometry from the selected features in the feature layer
          var spatialClauseGeom = spatialDefnLayer.GetFeatureOutline(MapView.Active, FeatureOutlineType.Selected);

DefinitionQuery definitionQuery = new DefinitionQuery
{
  WhereClause = whereClause,
  Name = $"{layerToQuery.Name}"
};
//Setting the spatial filter to the Definition Query
if (definitionQuery.CanSetFilterGeometry(spatialClauseGeom))
{
  definitionQuery.SetFilterGeometry(spatialClauseGeom);
}

layerToQuery.InsertDefinitionQuery(definitionQuery);
layerToQuery.SetActiveDefinitionQuery(definitionQuery.Name);

      var us_parks = map.GetLayersAsFlattenedList()
      .OfType<FeatureLayer>().First(l => l.Name == "USNationalParks");

      QueuedTask.Run(() =>
{
  var def_query = new DefinitionQuery("CaliforniaParks",
                        "STATE_ABBR = 'CA'");

          us_parks.InsertDefinitionQuery(def_query);
          //Set it active
          us_parks.SetActiveDefinitionQuery(def_query.Name);

          //or....also - set it active when it is inserted
          //us_parks.InsertDefinitionQuery(def_query, true);
      });

    var greatLakes = map.GetLayersAsFlattenedList()
                .OfType<FeatureLayer>().First(l => l.Name == "Great Lakes");
    var usa_states = map.GetLayersAsFlattenedList()
    .OfType<FeatureLayer>().First(l => l.Name == "US_States");

    QueuedTask.Run(() =>
    {
//name must be unique
        var def_query = new DefinitionQuery("GreatLakes",
                                                    "NAME in ('Huron','Michigan','Erie')");

        //create a filter geometry - in this example we will use the outline geometry
        //of all visible features from a us states layer...the filter geometry will be
//intersected with the layer feature geometry when added to the def query
        var filter_geom = usa_states.GetFeatureOutline(mv, FeatureOutlineType.Visible);
        //other options...
        //var filter_geom = usa_states.GetFeatureOutline(mv, FeatureOutlineType.All);
        //var filter_geom = usa_states.GetFeatureOutline(mv, FeatureOutlineType.Selected);

        //Geometry must have a valid SR and be point, multi-point, line, or poly
        if (def_query.CanSetFilterGeometry(filter_geom))
{
  def_query.SetFilterGeometry(filter_geom);
}

        //Apply the def query
        greatLakes.InsertDefinitionQuery(def_query);
        //Set it active
        greatLakes.SetActiveDefinitionQuery(def_query.Name);

        //or....also - set it active when it is inserted
        //greatLakes.InsertDefinitionQuery(def_query, true);
    });

//Must be on the QueuedTask
var url = "https://geoeventsample1.esri.com:6443/arcgis/rest/services/AirportTraffics/StreamServer";
var lyrCreateParam = new FeatureLayerCreationParams(new Uri(url))
{
  IsVisible = true,
  //At 2.x - DefinitionFilter = new CIMDefinitionFilter()
  //{
  //  DefinitionExpression = "RWY = '29L'",
  //  Name = "Runway"
  //}
  DefinitionQuery = new DefinitionQuery(whereClause: "RWY = '29L'", name: "Runway")
};

var streamLayer = LayerFactory.Instance.CreateLayer<StreamLayer>(lyrCreateParam, map);