To get free Bitcoin "gold", one just need to keep Bitcoins in exchange? Like for exemple did Kraken.com last time give Bitcoin Cash to all those who had Bitcoins?
ONLY IF the exchange you are keeping your coins in promises to support the fork and also promises to credit your new coins to you after the fork if you keep coins there. not all exchanges do this so make sure you check it out.
for example i remember asking c-cex about BCH and they said they will not support it so i made a withdrawal.
Relatively new in this world so don't know what happened in last fork. Or one need to keep them in particular bitcoin wallet to get free gold?
nothing special really. BCH forked from bitcoin and created an altcoin. some people got their BCH tokens out and enjoyed the free money, some others are still holding it because they have hope and some never bothered to claim it.
the "particular wallet" you need to keep your coins to get any futuristic fork new coins will ALWAYS be a wallet that you are the only one who has access to the private keys.