The most basic question I expect Sansa, Arya, and Jon to ask the Three-Eyed Raven is if he's still Bran or if Bran is dead. Because the strange, emotionless boy in front of them is very clearly not the adventurous, kind little brother they once knew. They've all been through stuff, but none of the other Stark children are behaving like robots. For that reason alone, they should be questioning this all-powerful being about what became of their brother. Is any part of him still Bran? Because the greatest tragedy for them is that they're looking at their brother, but he's not there at all.