I have been asked interview questions like these: "Tell me a technical project which was most challenging?" or "Tell me a technical project where you learned most?" or "Tell me about the hardest bug that you have solved?" This is also covered in the chapter "Behavioral Questions" topic "Know your Technical Projects" in the book "Cracking the Coding Interview by Gayle Laakmann McDowell"
What is the interviewer looking for? What are the data points or signals while evaluating this kind of questions?
Update: Behavioral Questions have a specific purpose. They are typically asked to gather data points from past behavior and predict future behavior. Although this is not an ideal solution but people or soft skills are very hard to evaluate. High Impact Interview questions explain this concept very well.
Many companies ask candidates to answer these questions in STAR format within 2-5 minutes (Tech recruiters of medium-big tech companies have shared this time limit in informal feedback).
Similarly, in Technical Behavorial questions, the guidelines are to structure the questions in challenges, architecture, tradeoff, tech stack, soft skill issues, hard bugs, etc.
What I am trying to understand is what behavior would be assessed?
(I am not a newbie in this area. I have many hit and misses in these kind of questions. Interviews are very short in time and Interviewers are always quick making judgement. I am trying to reduce failure by preparing as much as I can)