[creato]

I think it's a terrible interview question, unless maybe you're hiring an electrical engineer.

It's not something you can expect someone to reason through from the basics, and it's not something I'd expect someone to know unless they've worked on problems involving the technique.

[jacksonkmarley]

Seems like a pretty reasonable question for a job involving signal processing where the candidate has experience. Certainly that could be electrical engineers. In that context putting a signal into the frequency domain seems pretty basic actually. Knowing the caveats of sharp edged filters in that situation doesn't seem like outrageously obscure knowledge.

[Nimitz14]

It's blindingly obvious that you would only ask this to someone who should know it.