public string GeometryUri {get;}

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

    QueuedTask.Run(() =>
    {
//enumerate the layer's definition queries - if any
var def_queries = us_parks.DefinitionQueries;
        foreach (var def_qry in def_queries)
{
            var geom_uri = def_qry.GeometryUri ?? "null";
            var sr_wkid = def_qry.SpatialReference?.Wkid.ToString() ?? "null";
            var geom = def_qry.GetFilterGeometry();
            var geom_type = geom?.GeometryType.ToString() ?? "null";

            System.Diagnostics.Debug.WriteLine($" def_qry.Name: {def_qry.Name}");
            System.Diagnostics.Debug.WriteLine($" def_qry.WhereClause: {def_qry.WhereClause}");
            System.Diagnostics.Debug.WriteLine($" def_qry.GeometryUri: {geom_uri}");
            System.Diagnostics.Debug.WriteLine($" def_qry.SpatialReference: {sr_wkid}");
            System.Diagnostics.Debug.WriteLine($" def_qry.FilterGeometry: {geom_type}");
  System.Diagnostics.Debug.WriteLine("");
        }
    });