The answer is simple with many avenues.
You ask someone, or they tell you. Then to make sure, you get online and check it out. Trust, but verify.
What if I see something in a book? Copy it down, then you get online and check it out. Know that the person you read knew what they said.
If I went to a lecture and the speaker to sell something talked of an interesting point? Try to get at least three sources that verify the facts.
Is this starting to look redundant?
Real Simple. Before you go into an interview of any kind and say something, be sure to check it out so that you know.