Jetstar are not a oneWorld airline, so there is no entitlement to any oneWorld privileges at all. This means (amongst other things) no lounge access.
Reference:
https://www.qantas.com/au/en/qantas-...igibility.html
Section "Eligible oneWorld status", click on the # footnote:
# The flight number must be operated and marketed by a oneworldŽ carrier. A oneworldŽ marketed flight refers to a flight with a oneworldŽ flight number, eg QF1 or AA222. A oneworldŽ operated flight refers to the actual aircraft or 'metal' on which you fly, eg Finnair aircraft. Excludes oneworld connect partner flights.