Hi Ashish,
Reference between User and Staging Task is stored in a separate object - StagingTaskUserInfo retrieved by StagingTaskUserInfoProvider. In your handler you can:
- Get the TaskID from e.Task.TaskID
- Using StagingTaskUserInfoProvider find UserID by TaskID
- Using UserInfoProvider get user details by UserID
Or you can even merge these queries into one SQL query joining these tables.