The Serie A clash is available in most nations through the rights holders' online platform, if they have one. Your best bet is to check who is showing the game in your country, and if they have an online service or iOS/Android app to watch it on.
Napoli vs Inter: AS English live coverage
You can also follow all the action from Naples here with AS English, with our inimitable live coverage. We'll be building up to the action throughout the day before giving you a minute-by-minute account of the game as it unfolds.