When it comes to expressing agreement or certainty, there are many synonyms for the phrase "you know it." Some other options include "absolutely," "indisputably," "beyond doubt," "undeniably," "positively," and "without question." These phrases can be used in a variety of situations, whether in casual conversation or more formal settings. Additionally, using synonyms for common phrases can add interest and variety to one's speech or writing. So, the next time you want to express certainty or agreement, consider using one of these synonyms to add a little extra flair to your language.