Can iPhone X be set to show battery percentage on the status notch?
Currently, as of iOS 11.1, there's no way of showing the battery percentage by default.

One way to see the battery percentage is to pull-down slightly on the right 'wing' (with the battery icon).  Once the screen changes to the Control Center, you'll be able to see the battery percentage.


Another way to find this out is to just ask Siri.  You can say "What's my battery life" and the response will include the percentage of power remaining.  

The remaining way is to charge your iPhone.  When you charge it, the battery percentage is briefly displayed on the lock screen.