There’s no one correct answer to this. Don’t worry about what answer the interviewer wants to hear. Instead, focus on making your reasoning well thought out and convincing. Here’s an example:
“To me, user research, user advocacy, and empathy are the most valuable skills for a UX designer. We need to be willing to put ourselves in the shoes of the users and think in detail about what they want from the product, how and where they’d use it, what features would be beneficial, and what inconveniences or shortcuts we absolutely need to avoid.”