MacBook Pro 2016 Touch Bar usage in Windows 10 Boot Camp
I personally haven't had the chance to try so.
But this video from 9to5 mac shows the functionality of the touchbar in windows via bootcamp.
tips and tricks for the touchbar
Windows is mentioned at 6:50

As you can see, the brightness and volume keys are available.
And here is a picture of my new macbook in bootcamp showing the functionality of the fn button: