Follow the smell and you'll find it no problem
Alternatively, from my knowledge
339, 376, 393, 374, 372, from stand C in eddy ave
Probably also a few buses from Bondi Junction, hyde park, oxford st, coogee
If you're not sure, use this site
http://www.sydneybuses.info/
Or alternatively use the sydney transport app or tripview if you have a smart phone
You can always ask the bus driver "do you go to randwick race course"