Not understanding a hypothetical would go like this:
"How would you troubleshoot X?"
"Why, is X broken?"
"No, but imagine it was broken."
"If it's not broken why are you asking me that"
You don't need to understand the technical detail in the hypothetical, to extract search terms and research it.
The answer of "I dont know that system so I wouldnt know where to start" is failing the hypothetical. You have many starting points for all technical research. It means you cannot even imagine where to begin.
If you are so shocked by the appearance of technical term you don't understand, that you wont even take the first step of putting that term into google, you really shouldn't be applying for technical jobs.
The most common answer I get, if I fight the interviewee, and reposition it as a technical issue they do understand, is that they relay to me an anecdote from a time when they did complete the troubleshooting. IE, they still dont engage with the hypothetical, they just use recall.
It’s a question where you should preface if you don’t know, then make sure you’re game to just try.
People who answer with research/troubleshooting methodology, go on to be excellent employees.
People who dont attempt it, are generally unable to cope without handholding.
"How would you troubleshoot x"
"I havent done that before"
"Ok, but how would you approach the problem"
"I dont know sorry"