The task attributes: Parent Task Name and Parent Task ID are not available in the data warehouse. There is a task hierarchy table available but it is not used to show the parent task information.
Clarity 16.2*, 16.3. 16.3.1
In order to make these fields available in the Data Warehouse you can create calculated attributes and include those in the data warehouse.
An example is:
You can do the same for the parent_task_id
The fields then show in the DWH_INV_TASK table (DWH schema)