Yes, pure, distilled cognac is considered gluten-free.
Cognac is a type of brandy made by distilling white wine (derived from grapes) in oak barrels. However, be on the lookout for hidden gluten in cognacs that add flavorings or other additives after distillation. There is also a risk for gluten cross-contact in facilities that process products containing wheat, barley, or rye.
Common Brands for Cognac: