As a hiring manager, when I interview people I don't generally care if they don't know the answer to an interview question I ask* - what I care more about it is

As a hiring manager, when I interview people I don't generally care if they don't know the answer to an interview question I ask* - what I care more about it is how they respond in the negative. If they don't understand the question, I'd expect them to ask for clarification, or state they didn't understand it and then try to reason it. If they don't know the answer, again I like to hear their thinking. * Within reason; there are certain questions candidates for a given job should be able to answer!