Forget about getting a glass screen protector, which simply adds thickness and weight with very little benefit. I’d highly recommend getting a matte film screen protector for the iPad Pro instead. I’ve used one from iCarez for the past couple of years and it’s awesome.
Not only does the matte surface provide more resistance when using the Pencil, but it blocks just enough reflections to make it easier to use in brightly lit rooms. It also is easier to clean than the bare glass, imho. I can also say that it protected my iPad the one time it fell off a table onto a brick patio. The screen protector got damaged, but none of the scratches made it through the film onto the glass.