As others have said:
Expand on Witcher Senses, is it too obvious, or a lot left to interpretation
Expand on Fast Travel
Expand on Horses, mounted combat etc
Expand on climbing/jumping. How high can the white witcher jump?
Expand on combat, targeting/aiming for select body parts, legs, arms etc. Dismemberment, gore?
Expand on fighting monsters, no qte, Dragon's Dogma influenced boss fights?
Expand on difficulty levels.
Expand on potions, pre and during combat, alchemy etc.
Expand on combat camera, dialogue and cutscenes. Facial animation, character animation.
Expand on the feeling of the world. Dust, trees, grass swaying, foliage, birds, insects, wildlife etc
Expand on weather effects, and any affect it may have on the game world, combat, travel.
Expand on points of interest. How enticing are they and is there a story reason to visit them.
Expand on game saves, user interface and how they handle logging of quest, and keeping you up to date with the story.
Expand on size of villages, towns and cities. How does it compare to Assassins Creed etc
Expand on NPC's, interaction, and their day to day
Expand on graphics, how detailed is the world, how detailed are the interiors. How repetitive are the textures.
Expand on caves, mines etc and are they unique or do they look the same.
Does the world appear huge? Are the vistas as impressive as Skyrim.
How well during the demostration does the story seem connected
They talk about key characters standing out in some way, how so?
Does it look like they are on winner, and will be able to successfully implement the Witcher franchise in an open world?
Can they send me an E3 review copy. I will sign an NDA I swear?
I'm sure there is a tonne more to bring up