public bool IsNullable {get;}

QueuedTask.Run(() =>
{
  var firstFeatureLayer = MapView.Active.Map.GetLayersAsFlattenedList().OfType<ArcGIS.Desktop.Mapping.FeatureLayer>().FirstOrDefault();

  // create an instance of the inspector class
  var inspector = new ArcGIS.Desktop.Editing.Attributes.Inspector();

  // load the layer
  inspector.LoadSchema(firstFeatureLayer);

  // iterate through the attributes, looking at properties
  foreach (var attribute in inspector)
  {
    var fldName = attribute.FieldName;
    var fldAlias = attribute.FieldAlias;
    var fldType = attribute.FieldType;
    int idxFld = attribute.FieldIndex;
    var fld = attribute.GetField();
    var isNullable = attribute.IsNullable;
    var isEditable = attribute.IsEditable;
    var isVisible = attribute.IsVisible;
    var isSystemField = attribute.IsSystemField;
    var isGeometryField = attribute.IsGeometryField;
  }
});