How do I know that I know something?

You know that you know something via a faculty of the the human psycho-sensiblo-emo triarchy. This is embodied by the sum called the Spirit. When knowledge is obtained, these faculties converge to have your reasoning, emotions and sensibilities tune in to a specific wavelength of understanding that one has obtained an additional component for sentience and that one moves closer to unity to the overall collective unconscious.

This phenomena is what we call "Googled".