If a person with a normal attitude receives a question to which he/she doesn't have an answer to, a reply would be "I have no idea. Why don't you look up the internet?" or "I don't know."
Know-it-all is the word describing;
A person who behaves as if they know everything
from Oxford Advanced Learner's Dictionary.
Someone who thinks he knows everything and refuses to accept advice or information from others.
Know-it-all can be used as an adjective.
8 Tips for dealing with a know-it-all coworker.