Other than straight, on the rocks. Which is also perfectly acceptable.
Wait, what is Fernet Branca?
Fernet-Branca is a dark liqueur with a bitter, black licorice flavor. It was originally invented in Italy in 1845 as a stomach medicine. These days, its actual "medicinal" properties seem suspect — although, lots of people swear that it's a magical hangover cure — but it's a great spirit in its own right, and just a little bit adds a whole lot of flavor to a cocktail.
Fernet and Ginger
The recipe calls for store bought "ginger syrup," but here's how you could make it at home. Recipe here.
Forgetfully, Fernet
A citrusy, gingery whiskey drink with a licorice-y twist. Recipe here.