I bought a ticket from Fiji to Europe from Cathay airlines but it involves both Cathay and air Pacific. I stop over at Sydney from Suva. I don't need a transit visa but need to recheck my baggage from Sydney to Europe because I change carriers. Can this be done without leaving the transit lounge?
Fiji Airways (also known as Air Pacific) is a Oneworld "Connect Partner", while Cathay Pacific is a Oneworld member. They also have codeshare agreements.
As long as the two flights are on a single ticket, you should be able to do through check-in of your luggage to your final destination, and will not need to reclaim and re-check it in Sydney. You should not need to go through immigration (passport control) or customs.
Provided you are within the conditions for transit without visa, you won't need a visa.