Dynamic upload location for Super Table within a Matrix field?
Have you tried using {owner.owner.slug}? If you've got Matrix > Super Table > Asset, and you're trying to get an attribute on the Entry/Element, you'll need to go two level out from the Super Table field.

Entry
  Matrix
    Super Table
      Asset Field


The owner of the Super Table field is the Matrix field. The owner of the Matrix field is the Entry.