How do you sau in French?

The word "sau" doesn't exist in French. It's possible you are thinking of a different word or phrase, or perhaps you have a typo.

Could you please provide more context or information?

For example:

* Are you trying to say "I know" in French? That would be "Je sais".

* Are you trying to say "save" in French? That would be "sauver".

* Are you looking for a French word that means "sauce"? That would be "sauce".

Please let me know what you're looking for, and I can help you find the correct French word or phrase.