The Bitcoin forked coins can be collected by importing your private key into a supported fork wallet.
You can export your private key by typing this command in the console: "dumpprivkey <your bitcoin address>", of course without
quotation marks.
It might be needed to decrypt your wallet first by "walletpassphrase <your-wallet-passphrase 300>", which will decrypt your wallet for 5 minutes.
Make sure you find the a suited wallet on the fork's authentic website so you don't lose both of your balances.
Thanks for your advice.
I wonder how can I get all my bitcoin addresses?
I also heard that it is recommended to transfer btc to another address before claiming forked coins.
To list all address use the command "listreceivedbyaddress", this will list all addresses that already have received transactions.
It's recommended to transfer your BTC to a new address, with a new private key. To prevent your coins from being stolen through a replay attack, although a patch has been implemented in most wallets it's still a good thing to do. Because your BTC still could get stolen when you import your private key in a malicious client or when your keystrokes/data get tapped.