Not the OP but I'd expect the desired answer to be some kind of semi-technical discussion that shows they understand the fundamentals even if they've forgotten all the details and can have a healthy conversation, not that they know the answer.

Possible good indicators: "I haven't written C code in a decades, but one is a byte, one is a structure" "I'd be in over my head with Unicode but.." "What are you looking to solve?"

Bad indicators: Hostility. Authoritative wrong answers.

(For a director of Product role once, I was asked the difference between REST and SOAP -- not because he cared that I knew the answer, but because he wanted to see how I could work with an engineer who was focusing on the wrong problem)