There's not one "right" word, and it's obnoxious and ignorant to insist otherwise. (Personally I think "coke" sounds stupid, but it's as legit as any other.)
My grandfather is called 'Pop'.
Soft drink. People would know what you're talking about if you said 'fizzy drink', but that's not in fashion. Soda, coke and tonic are actual specific drinks.
Soda. Objectively the only proper word for it.