The transaction is first filtered in the following way and then sent to non-validating notary service:
stx.buildFilteredTransaction(Predicate {
it is StateRef || it is TimeWindow || it == notaryParty
})
The notary service will see:
Any inputs, in the form of StateRefs
The time-window, if it exists (since the notary is also the timestamping authority)
The identity of the transaction's notary