Bitcoin Forum

Sorry newbie, but growing fears about another fork in November.  I guess similar question to the Bitcoin Cash ordeal which I missed.

Would your private key exist on both chains?
How do you know if you have a wallet that will support both coins in case you wanted to cash out?   (For example something like Coinbase.)
How would you access and trade the resulting 'alt' coins?

Just treat them the same as any other new coin. Say that Bitcoin forks and becomes BTC2, there are obviously differences, if you would buy that coin with the changes, then keep your coins, otherwise, sell.

if there will be two chains then yes. since the chains need to be backward compatible, the private keys and all the transactions up to the point of the fork will be valid on both chains.

something like coinbase is not a wallet exactly. and you need to ask them, but they usually make a clear statement when things are close and clearer. just like they did back in July (before the August fork).
if you have your private keys you have your coins. if you don't see a private key (like in Coinbase) you own nothing but a promise.

as for trading you should see which exchanges list them. for example BCH was listed on bittrex from early days. other unknown exchanges like ViaBTC also had it but they are never trusted enough.

You can redeem the forked coin easily if you own bitcoin in your desktop wallet such as electrum.Don't keep your coins in a web wallet such as coinbase because they can decide to keep for themselves the forked coin or take time until they release it.
I take my self as an example,I was using Xapo wallet during 1st August fork.Until now they still didn't release our bitcoin cash.They take a very long time to release it to users.

Good luck  :)

Yes.
Coinbase is not a real wallet, so in their case all you will see is whether they have an interface that allows you to spend the coin on the new chain.  You'd have to find announcements by them about what they intend to do in the fork and ideally withdraw to a wallet where you control the private keys.

In a proper wallet, it doesn't matter because you can always export your private keys to another wallet which will give you that interface or you can send BTC to another wallet and then export the private keys to a wallet for the new chain.
Depends on whether the chain has replay protection.  In BCH's case, you could send away the BTC and export the private keys to a BCH-compatible wallet and then send normally (or if you have a compatible wallet, spend both freely when handled properly).

You should read about the possibility of SegWit2x replay attacks (https://cryptoinsider.com/replay-attacks-explained/) and keep an eye out for any warnings on bitcoin.org or this forum in case it's unsafe to send coins during the time of the fork.