The fuel economy of a SVT Mustang Cobra varies significantly depending on the model year and driving conditions. However, you're generally looking at figures in the
low teens for city driving and perhaps the
mid-to-high teens on the highway for most model years. Don't expect anything close to modern fuel efficiency standards. You won't find any official EPA estimates in the high 20s or 30s like many modern cars.
To get a more precise estimate, you'd need to specify the exact year of the SVT Cobra.