Here's a breakdown:
* De qué: This is a contraction of "de qué," meaning "of what" or "what is it made of."
* es: This is the verb "to be" in the third person singular present tense.
* la chaqueta: This is the feminine definite article "la" followed by the noun "chaqueta," meaning "jacket."
So, the entire phrase is asking about the material composition of the jacket.