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For connections from Qantas Domestic to Jetstar International flights, baggage transfer is provided.
See the Jetstar web site Airport Information page here. Then read the second paragraph under "Flight connections, baggage transfers and Recommended Connection Times" and click the "click here" link at the end of that paragraph to get a table that shows under which conditions baggage transfers are provided. You will see that QF Domestic to JQ International does provide baggage transfer.
Try and get the bookings linked (call QF) and be explain that you are connecting to the checkin staff and make sure your bags get the right tags, otherwise you may be in trouble. If the flights are on the same booking you would have no issues.