Ugh, I know someone (thankfully no longer a current colleague) who ardently *defends* his use of questions like "what does the -M option to ps do?" on the basis that "any senior person who knows what they're doing should know all the options to ps!". No, you useless tit, anyone who knows what they're doing should know how to read a bloody manpage.
Beyond that, if by "Senior" the role is the one the other tech people turn to when they're out of knowledge/skills/ability, there's just too much breadth to remember every detail about every tool. Quite the opposite from remembering every option to a tool, it's impossible to even keep track of every tool. The job as "senior" people is to figure out the stuff that we don't always know within that company. The main benefit of questions for HR to ask is the bozon filter: make sure it's actually someone who does network, or systems, or database, or whatever work. If one question (or even 10) could reveal the level of responsibility someone were capable of, we wouldn't need the interview process.