Should be able to do this in a report. You would report on the rm_scrum_task table, like you are already, then in the filter conditions select Parent, hit the arrow next to it, then click State. Then choose is not, or is not one of, and select the states you want it to look for, then hit Run. This will return all Scrum tasks where the Parent is not whatever states you selected. Here is a picture of what that would look like