When it comes to someone who always believes they know everything, we often use the phrase "know all the answers" to describe them. But there are other synonyms that can be used to convey the same meaning. For instance, you could say that someone is a "know-it-all", "wiseacre", "smart aleck", "busybody", or "braggart". Additionally, you might say that someone is "overconfident", "arrogant", "cocksure", or "hubristic". Regardless of the word that you choose, the point is the same-- that this person tends to express their opinions as absolute facts and fails to consider other perspectives or ideas.