She doesn't want to place herself directly into the conflict that Kylo and Luke seem to have been deliberately avoiding, but she wonders how much either of them have said to Vader about it, or how much he might've picked up on. It's a discussion for another time. As are tales of the Sith; Rey's still too raw from the Palpatine reveal to want to hear about anything to do with Sith powers.

"Something you said before -- you and Obi-Wan were Force-bonded, right? Are you still, after everything?"

She's not asking to pry; it's just that she's long wondered what might manage to sever the bond between herself and Kylo. Once it would've been to attempt to break it herself. Now it's something else entirely. If nothing else, she believes they're going to need this strangely overactive bond to help them defeat her grandfather.