30 Rock Season 4 Episode 22 (30 Rock s04e22) with title “I Do Do” airs on Thursday, May 20th 2010 at 09:30 pm via NBC.
Here is summary for 30 Rock Season 4 Episode 22 :

Wedding bells ring in the Season 4 finale when Liz juggles going to three different nuptials, all while meeting her Mr. Right. Meanwhile, Jack’s chaotic love triangle reaches its decisive moment.

Few hours after original series aired on TV, online streaming video for 30 Rock Season 4 Episode 22 usually available on Net and of course, if video available, as soon as possible will show you where you can watch this episode for free.