It depends on which version of the rules you are playing with. It's 4 points (2 for the city and 2 for the shield) according to First edition rules and 6 points (4 for the city and 2 for the shiled) according to 3rd edition rules.
If you use 1st edition rules, shouldn't the city in question score 3 points? In all other cases, the pennants are worth the same amount of points as the tile (2 for regular cities, 3 for a city with cathedral). Logically, a city with two tiles worth 1 point each should score 1 more point for the pennant = 3 points in total.