Promesa

The TV can be found on the 14th level using stage select (Thumbnail is of a blue sky with clouds) the location seems to be random each time but you can easily locate it by listening for the sound it makes. Simply find the TV within 40 seconds to unlock the achievement. While you're there you can also sit through all of the Ads on the TV and unlock the Pubblicità achievement as well.

I show one of the locations in my Achievement Walkthrough starting at 1:50 in the video.

After beating the game you unlock stage select.
The 14th stage is a cloud level. You need to find the TV in the stage with 40 seconds

See in video at 7:20

Achievement Walkthrough:

Located on the fourteenth level if you're doing Scene Selection, otherwise it's the Cloud level. Begin by going straight ahead until you find the TV and the couch. As long as you do it in under 40 seconds you'll unlock the In the Clouds achievement. This is randomly generated if the TV will spawn straight ahead of you, in my first playthrough it did but when I was doing achievement mop up it was to the far left. Either way you should get this during one of your visits to the level. After you find the TV you'll get warped to the cave area with the television, simply keep watching it until you've watched all of the commercials and the Pubblicita achievement will pop. This took me about three minutes.

I HIGHLY recommend finishing the level instead of quitting out. When I quit out my Scene Selection option vanished. Luckily I was able to quit out and reload the game to make it appear, but you do NOT want to risk another playthrough of this game.