If you own Bitcoin, the fork won't affect what you have. All that will happen is that there will be an additional coin called Bitcoin Gold that will exist parallel to Bitcoin. If you control the private keys to your Bitcoins, you will also own the Bitcoin Gold fork. All you have to do is claim those coins. However, there is no guarantee that Bitcoin Gold will be worth anything. On the other hand, I'm sure there are those that would say that there is potential that Bitcoin Gold could become the dominant coin and I suppose that is a possibility but it is unlikely.