On my recruit playthrough, the first level where I saw a dog that actually attacked me was on SAFEHOUSE. Load the mission up and progress your way up the hill. Right around when you get to the burning building, a dog will come running down the hill. Let the dog jump at you 2-3 times (remember recruit difficulty) and it will eventually knock you down to the ground. With the dog now on top of you, wait for the command prompt to snap the dogs neck. I'm using tactical button layout so this prompt button for me was to click RIGHT JOYSTICK, Don't click the prompt too late or too soon, otherwise your neck will become dog food.