The synced record Task has a self-referential relationship defined in the column parentTaskId.

Create a sync-time custom record field on the Task record called parentName. Specify this field to return in the query field selection.

Use a!queryRecordType() with a filter on the task id, with fields specified to return recordType!Task.name and recordType!Task.parentTask.name.

Use a!queryRecordType() filtered on the task id once to return the task name and parent task ID. Query the record again to return the parent task name.