The best technical question I've had so far was after the phone screen the hiring manager emailed me a question that I needed to solve in 2-3 days. During my investigation on how to solve the problem I discovered I would need to implement a K-D tree. I don't have a CS background so I just found some open source implementations of a K-D tree.

I sent the manager an email telling him that I couldn't write a K-D tree on my own, but I would use the implementations that I found online to solve the problem. He replied that what he was looking for was someone who would've relied on an existing solution to solve the problem instead of trying to code it all from scratch. So I passed his test and was called in for an in person interview which was just trying to see if I would fit in with the team. It all worked great and I was hired. I didn't have to do anything with a whiteboard.