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());
}