which episode is titled g.g in this tv series?
The thirteenth episode
G.G. (Gossip Girl)
the thirteenth episode 
who does blake lively marry in gossip girl Penn Badgley
wiki:19800062
G.G. (Gossip Girl) [SEP] Introduction
"G.G." is the thirteenth episode of the fifth season of the American television teen drama, "Gossip Girl" and the show's 100th episode overall. The episode was written by executive producer Joshua Safran and directed by Mark Piznarski. It premiered on The CW Television Network (The CW) in the United States on January 30, 2012. In the episode, the wedding of Blair Waldorf (Leighton Meester) to Prince Louis Grimaldi (Hugo Becker) takes place. The episode opened to favorable reviews, with television critics praising the fact it honored the series' successful days. Michelle Trachtenberg's performance as Georgina Sparks was also well received.