On the e-ticket it has along with other pages of information it states "Interline travel: Qantas baggage allowance may not apply. If your travel on this ticket involves more than one airline, the baggage allowance of the most significant carrier in your itinerary will apply to each journey, except in relation to travel to, from or within the USA" which would be JetStar as the significant carrier. I don't know what to believe as the e-ticket also has pages on luggage which includes:
QANTASLINK SERVICES All customers 1 piece at 23kg (50lb)
Jetstar ECONOMY Starter, Max fares and Classic Flight Rewards (booked after 15 February 2023) where the flight number starts with "JQ" All customers 1 piece up to 23kg (50lb) total (no piece limit)
which all point to 23KG allowance.