When the app starts, press to move over to ‘Library’ and select ‘Interactive Episodes’.
This is unlocked in Episode 5, ‘Humpty’s Big Break’, Chapter 4, ‘Clap for the Letter D’.
When a letter appears on stage, if it is the letter ‘D’, clap until the clap meter is full. The letters that show up in order are: D, G, D, B, D.
The simplest way to unlock this achievement is using ‘Chapter Select’ to choose the chapter. When the chapter is over and the next one starts, just press , move over to ‘Stop’ and press again. The achievement will unlock when it is buffering. You can alternatively watch the entire episode, but that would be more time consuming.