G'day Rebekah,

You will need his full name and service number. If you don't have that you can search for them here: http://www.ww2roll.gov.au/
When you have full details you can then do a search and request a copy of his service records from the National Archives of Australia here:
http://www.naa.gov.au/collection/explore/defence/service-records/army-wwii.aspx

Cheers,

Ted