Here's a breakdown of the errors and how to correct them:
* "Tu cest" should be "Tu sais" which means "You know."
* "Paerler" should be "parler" which means "to speak."
* "Francies" should be "français" which means "French."
The correct way to ask "Do you know how to speak French?" in French is:
"Sais-tu parler français ?"
This is a more formal way to ask the question. A more casual way would be:
"Tu parles français ?" which means "Do you speak French?"