Which of the following grape varieties is NOT used for making Cognac?

Pineau Blanc is not one of the grape varieties predominantly associated with the production of Cognac. Instead, the primary grapes used in Cognac production are Ugni Blanc, Colombard, and Folle Blanche. Ugni Blanc, in particular, is the most significant grape variety used, known for its high acidity and ability to produce high-quality, aromatic eaux-de-vie. Colombard and Folle Blanche are also integral to constructing the character of Cognac but are less commonly used than Ugni Blanc today.

While Pineau Blanc might be cultivated in some regions, it is not recognized as a key grape for Cognac's production. Thus, labeling Pineau Blanc as not used for making Cognac aligns with the understanding of the specific grape varieties integral to creating this iconic spirit.