From what I can tell, that's the only question left which the Republicans think is appropriate for Democrats to ask in his confirmation hearing. It's apparently unfair or obstructionist or illegal or something to know anything relevant about a guy who's about to be appointed to a lifetime position on the Supreme Court.
It's weird, really, that the Right wants to nominate people to the Supreme Court whose opinions are as unknown as possible and then make it impossible to know them. They've turned Roberts into Schrodinger's cat, locked him in the box, and then argued if we take a peek inside we might find out that he's a dangerous wingnut and the nomination would be killed. Better, then, to leave Roberts in a state of quantum wingnut indeterminacy, a superposition of wingnut and non-wingnut.