public IEnumerable<TaskInfo> GetTasks()

var taskItem = Project.Current.GetItems<TaskProjectItem>().FirstOrDefault();
// if there isn't a project task item, return
if (taskItem == null)
  return;

string message = await QueuedTask.Run(async () =>
{
  bool isOpen = taskItem.IsOpen;
  Guid taskGuid = taskItem.TaskItemGuid;

  string msg = "";
  try
  {
    TaskItemInfo taskItemInfo = await taskItem.GetTaskItemInfoAsync();

    msg = "Name : " + taskItemInfo.Name;
    msg += "\r\n" + "Description : " + taskItemInfo.Description;
    msg += "\r\n" + "Guid : " + taskItemInfo.Guid.ToString("B");
    msg += "\r\n" + "Task Count : " + taskItemInfo.GetTasks().Count();

    // iterate the tasks in the task item
    IEnumerable<TaskInfo> taskInfos = taskItemInfo.GetTasks();
    foreach (TaskInfo taskInfo in taskInfos)
    {
      string name = taskInfo.Name;
      Guid guid = taskInfo.Guid;

      // do something 
    }
  }
  catch (OpenTaskException e)
  {
    // exception thrown if task file doesn't exist or has incorrect format
    msg = e.Message;
  }
  catch (TaskFileVersionException e)
  {
    // exception thrown if task file does not support returning task information
    msg = e.Message;
  }
  return msg;
});

ArcGIS.Desktop.Framework.Dialogs.MessageBox.Show(message, "Task Information");