Search: Find Items by Permission Sets
This will find all Content Items where the field is available but has no value, where no Permission Sets are applied.
CODE
-_exists_:permissionSetIds
This will find all items of the specific Permission Set.
CODE
permissionSetIds:787eb87f4c914ec5ba359cc8d8a1d0af
The Permission Set Id is shown in the URL in the Permission Set Detail View: