A User for the 'Parent' Account of a Buyer Organisation (i.e, Accor, IHG, Iconic, Crystalbrook, etc.) who is set up as an Approver at the 'Parent' level, will be able to see all Invoices that need approval, at both 'Child' and 'Parent' levels.
(Note - the full scope of visibility depends if the User is a Financial or Operational Approver).