You may not have seen it as it folds up and slides behind the last row of seats on the 2 seat side of the A/C. It's kind of complicated to unfold and set up if you've never done it before. Be sure and ask the working F/A for a tutorial.
BTW, since it blocks the lav entry when it's out, usually the working F/A will ask you to get up and fold it away once above 10,000 FT and then you can sit in the main jumpseat while they perform their service.