Answer: Understanding and nonjudgmental.
Explanation: if I were listening to a Friend who had a problem and was telling me, I'd want her to know that her problems and maybe secrets where safe with me and I would also have here know that I wouldn't judge her or her choices.
This would make her more relaxed and open. The aim of listening to her problems should not be just to listen but to try and offer a solution. So while she speaks, it would be nice to listen attentively and objectively so that at the end of the conversation, I could offer a solution.