If your Bitcoin is
on an exchange, some Bitcoin exchanges such as Kraken in Europe does not plan
on supporting Bitcoin
Gold, of course they might
change their
minds if it becomes more prominent, but if you don't control your own keys it might be difficult for you to get to a Bitcoin
Gold after the split, but if you have your own private keys, for example in a hardware wallet or something like co-pay
on your phone, then you will be able to claim your Bitcoin
Gold at a later date at least in theory.