Actually, I just did mine yesterday!
I think the questions vary across examiners and obviously they're mixed up, but there's a list of expected things to know for the general knowledge component of your Grade 8 AMEB piano exam: ameb.unimelb.edu.au/wp-content/uploads/2013/09/General-Knowledge-Guidelines.pdf
The questions that I got asked were:
What period was ___ piece composed in
What form is this piece?
Does ___ composer have a 'style'? Describe the style
What other works were composed by ___ composer?
Any key modulations?
etc.
Good luck for yours!