This is a pretty hard problem I haven’t solved just yet. Generally, my in person interview is based on a set of DS problems I’ve been working on and had to do research myself to solve. What I look for is a strong intuition of the underlying math. Like, I can give them a formula and they can intuitively express what that means and explain it to me and then explain the next place they would take the solution. It’s not a perfect measure, but i’ve found the comfort with core concepts to be the most common trend among great data scientists I’ve worked with in the past.