Hi,
the answer to your question depends on what you are really expecting on the subtasks.
Do you want to see the exact same information that you have on the parent task, also if the fields are edited on the parent? If yes, I would suggest to create a second custom form, which consists of calculated fields referencing to the fields of the custom fields on the parent task.
Example:
{parent}.{DE:fieldName}
The other possibility would be to create a Fusion scenario, which copies the field values from the parent to the subtasks.
Put simply, the values of your custom fields are saved in a separate database table and linked to the respective object to which the corresponding form is attached.
So, the exact same value would be saved multiple times to the database, once for the parent task and for each subtask.
If someone edits the field on one of the tasks, the others will not be updated.
Regards
Lars