"I know everything."
Translation:Ich weiß alles.
There's a difference in meaning between "wissen" and "kennen" even though they can both be translated as "to know." "Wissen" means to know a fact, like "Ich weiß, wie alt er ist" - "I know how old he is." The age is a fact that I happen to know. "Kennen" is means something more like "to be familiar with." You would use this when talking about knowing a person, z.B. "Ich kenne dich" - "I know you." But you would also use it to ask something like "Kennst du den Film?" - "Do you know the film?/Are you familiar with the film?"
"Wissen" is the infinitive of the verb "to know" and its conjugation is irregular. It conjugates like this: ich weiß, du weißt, er/sie/es weiß, wir wissen, ihr wisst, sie/Sie wissen. "Weißen" is a completely different verb which means "to whiten" or "to whitewash" and just looks like some of the conjugations of "wissen."