Bitcoin gold is the result of the hardfork of bitcoin this October 25th, so you are going to receive free bitcoin gold on your wallet, but only if you wallet accepts/supports bitcoingold.
Anyway, you will receive 1 btg per 1 btc that you have on the same time, just like it happened with bitcoin cash on the last fork of August 1nd, so probably you know how it was and how it will be.
try to hold your bitcoins on a safe wallet that you know that is going to give you bitcoingold.