What is the capital of Austarlia?

There is no second capital of Australia. Australia's first and only capital city was and is Canberra.
Each of the states has a capital city, as does the Norhern Territory, but Australia's Federal capital has never been any city other than Canberra, the site for which was namd in 1908.

There is a common misconception that Melbourne was once Australia's capital city, but this was never the case. It was only ever the temporary seat of power, as it was the only city with a building large enough to house Parliament whilst Canberra was being built.