Ask HN: What questions should I ask my “Show HN” users?

Few days ago I was on [HN homepage][0] for a few hours with my https://refjar.com project. 81 users registered an account, 41 bookmarked at least 1 item, 2 users bookmarked 9+ items.

What do you think are the best kind of questions I should ask these people to help me move with refjar into the right direction?

[0]: https://news.ycombinator.com/item?id=16984532