What do MPs ask their questions for oral answer about? They Work For You has compiled some statistics, reproduced below:
As you'd expect, the PM is first, as a basic issue of government accountability, and the big portfolios of health, education and justice feature heavily. Finance is near the top because of constant questions about taxes, justice because of the EFA. Immigration and corrections however seem to get vastly disproportionate coverage, likely due to their being knee-jerk issues.
It will be interesting to see how the chart changes in the next Parliament.