public bool CanLookupSymbol()

{
    //feature layer from the active map
    var featureLayerLookUp = MapView.Active.Map.GetLayersAsFlattenedList()
                            .OfType<FeatureLayer>()
                            .FirstOrDefault();
    //Get the selection
    //Note: Needs QueuedTask to run
    var selection = featureLayerLookUp.GetSelection();
    //Get the first Object ID
    var firstOID = selection.GetObjectIDs().FirstOrDefault();
    //Determine whether the layer's renderer type supports symbol lookup.
    if (featureLayerLookUp.CanLookupSymbol())
    {
        //Looks up the symbol for the corresponding feature identified by the object id.
        var lookupSymbol = featureLayerLookUp.LookupSymbol(firstOID, MapView.Active);
        var jSon = lookupSymbol.ToJson(); //Create a JSON encoding of the symbol
                                          //Do something with symbol
    }
}