First of all make sure you have Developer Commentaries turned on in the options, as it seems to be turned off by default. You can find lots of these in any levels, but sticking with how most did it on the 360, we'll go with the DLC level, Dosan's Tale.
By the first enemy, just hanging in the air, you'll see a speech bubble. Either kill the enemy and jump up and press
to read it, or just hit it with a dart.