For example, one I like to ask (in person, with no computer access), ostensibly to gauge familiarity/intimacy with the Unix CLI, is:
"For each letter of the alphabet, see if you can name a Unix command (anything one can type at a shell prompt that won't return a "command not found error") that starts with that letter."
I preface the question with something suggesting that it's supposed to be fun, and I encourage skipping letters and coming back to them to avoid pressure (nor do I write down the answers). Most people are surprised at how many they remember without much thought.
Although not particularly deep, further discussions can arise from differences between shells with respect to built-in commands, as well as differences between OS flavors. Also, I've discussed how a somewhat new language like Java has made one of the otherwise difficult letters much easier.
Regardless of the trivial nature of the question/exercise, it provides a spectrum of jumping-off points for deeper knowledge discussions, all of which are signaled/chosen by the candidate.
Currently, many interviewers go for - as I like to call it -"trivia questions". Personally, it just doesn't seem appropriate because "Everything may be obvious, once you know the answer". In some such interviews, I've asked my own set of trivia questions to the interviewers. The interviewers weren't pleased as they couldn't answer some questions for which I knew the answers beforehand.