How do you say i know what am saying in french?

Here are a few ways to say "I know what I'm saying" in French, with varying degrees of formality and emphasis:

Formal:

* Je sais ce que je dis. (This is the most literal and formal translation.)

* Je suis certain de ce que je dis. (This emphasizes your certainty.)

Informal:

* Je sais de quoi je parle. (This is more natural in everyday conversation.)

* Je sais ce dont je parle. (Similar to the above, but slightly more formal.)

* Je sais ce que j'affirme. (This emphasizes your confidence in what you're saying.)

Emphasis:

* Je sais très bien ce que je dis. (This emphasizes that you are fully aware of what you are saying.)

The best choice will depend on the context and your relationship with the person you are speaking to.