Outside of the context of job interviews, I find when talking informally with someone who truly knows a shitload, they tend to know enough to know how much more there is to know and may make mention of that along the way. And those that don’t know how much they don’t know of course can’t really mention that because they can’t even convince of all the stuff they don’t know.
I always pay attention to people who are like the former and who are comfortable with maintaining an appropriate level of uncertainty because it usually means they think more scientifically.
Or put another way, he who speaks loudest knows least.