There is a local in Palermo called Ferneteria, which has plenty of varieties you can explore, and a decent bartending staff to make it how you'd like. As a veteran craft bartender, my own personal addition of info is that Branch is the superior of them all, although depending on your mixer or cocktail you might find another one more suited to your liking. Tradionially, Amaro in general (all fernets, Cynar, Averna, etc.) are digestifs, and therefore usually enjoyed neat. That being said, its more important to have it the way you enjoy than the way you "should", which goes for all beverages (I quite love how a glass of ice is served house white wine in most establishments without having to be ordered specifically).
As far as the mixing it with Coke goes, while normally I would agree that adding a spirit to coke is for subpar quality distillates, in this case I find it to be the rare exception. Coca Cola is a non alcoholic fernet in a way, utilizing many of the same herbs and spices used in Fernet. Or I guess you could say fernet is an alcoholic Coca Cola, albeit less sweet and more bitter. To that regard, they compliment each other in a way rivaled by few other highballs. Certain good quality gins are made better when served with good tonics, and I find this to be the case here. Each one is close to each other but fill in the notes the other is missing. And while normally a HUGE proponent of an almost equal booze to mixer ratio, with Fernet and Coke I find that a weaker one actual balances out better in flavor profile.
A traditional sour (with egg, fresh lemon, and sugar) is also another way Fernet shines through nicely.