When playing the game, be aware of the bottom left corner of the screen. An image of the controller's back button and the name of a skit will appear at various times and when pressed will launch one of these skits. Some of them are only available briefly so be sure to always hit the button right away when you see it. There are about five hundred of these and some won't show up until you use certain items/skills or do certain quests.
You can spend 1000 in the Grade Shop to unlock a skit viewer and every skit. The skits you missed will be a very light blue color and you will simply need to view those in the skit viewer at Nam Cobanda Isle to finish this achievement. You can hit start and select "yes" to skip the skit and still get credit for watching it.