This encounter can be found by searching 'event space' around the San Diego Convention Center. You can also reach the San Diego Convention Center by purchasing City Pass: San Diego in-app.
It is actually simply called "Comic Con" in the game, but I have titled this with the 2014 as it is possible/hopeful that Ed will give us one in later years too ;).
With this encounter, you simply need to approach the sounds of fighting, and then help the survivor who is surrounded by a horde. From memory, you will be facing a horde of 30 zombies, so equip your best gun. Afterwards, you can ask Keegan to join you. Keegan will also give you a HK45C gun. He also comes with one.
SPOILER: I have added the photos of the encounter below, as this is a time limited encounter that will soon disappear, and then we will lose this storyline.
