public ReadOnlyObservableCollection<Layer> Layers {get;}

public async Task ObtainingGeodatabaseFromFeatureLayer()
{
    IEnumerable<Layer> layers = MapView.Active.Map.Layers.Where(layer => layer is FeatureLayer);

    await ArcGIS.Desktop.Framework.Threading.Tasks.QueuedTask.Run(() =>
    {
        foreach (FeatureLayer featureLayer in layers)
        {
            using (Table table = featureLayer.GetTable())
            using (Datastore datastore = table.GetDatastore())
            {
                if (datastore is UnknownDatastore)
                    continue;

                Geodatabase geodatabase = datastore as Geodatabase;
            }
        }
    });
}

public void SelectAllFeatureLayersInTOC()
{
  //Get the active map view.
  var mapView = MapView.Active;
  if (mapView == null)
    return;

  //Zoom to the selected layers in the TOC
  var featureLayers = mapView.Map.Layers.OfType<FeatureLayer>();
  mapView.SelectLayers(featureLayers.ToList());
}