Will there be a hard-fork between B2X and BTC?

Yes, most likely, although it's hard to know for sure. There seems to be enough people who want the 2x fork that it will happen, and there definitely are people who will continue running Bitcoin Core (which is the form of the bitcoin protocol that will stay with the current block size), which will create two separate chains. There is a really good debate on this fork that took place recently that you can watch here

How can we know for sure? When will it occur?

We will know for sure once we get to block 494,784 which is when the fork is scheduled to happen (sometime around Nov 16). You can view the current block number (usually referred to as "block height") over at blockchain.info. Watch for news around that time about what is happening. Coindesk is a good resource for that.