Congratulations on getting an invite, I guess you're an Australian with a HK Visa?
Either way, a COMPASS test is the same regardless of what institution you sit it at and I'm aware of two websites that can be used to practise for the battery of tests that are included.
You have CockpitWeb which I believe has been around for a number of years, has been awarded by FlightGlobal in the past but is becoming slightly outdated, and tends to focus on only PILAPT (which, although the same, has a fair amount of differences.)
Cockpitweb: pilot aptitude test,Pilot computer test software,numerapt,numerical reasoning, psychometric test, mathematics,job application,pilot recruitment,IFR Training Software, ATPL Pilot Training, Pilot Training flight simulator, aviation training
And there is PilotAptitudeTest, which looks to be a much newer website, providing both COMPASS and PILAPT practice; and also includes a system that allows you to compare your performance against others, useful considering the real tests are scored from a database of candidate averages.
PAT | PilotAptitudeTest.com - Practise for COMPASS Tests and PILAPT Tests
If you prefer a paper-based format, check out your local pilot supply shop, as they may have books specific to Jetstar interviews and aptitude tests.
Best of luck with it.