There are 100s of songs that use these two chords together in a progression because it very easy to change from Cadd9 to G. Simply keep your 3rd and 4th fingers on fretboard when you change chords. It is also very common to have song progression with G, Cadd9, and D.
Play this progression slow and clean at an even tempo, repeating.
You need to really focus on the songs below. Get so you can play the songs really good before you move on to the next lesson. Remember, this will take a lot of hours of practice and a lot of patience. Hang in there!