Can anyone tell me if the cast of SDR2 is the same as that of the Despair Arc, cause i want to start watching the Despair Arc, but i haven't fully read the SDR2 manga?

do tu happen to know where I can read the whole manga cause I can't seem to find it

There are many manga variations for SDR2. The only one which follows the main story accurately is called SUPER DANGANRONPA 2 - SAYONARA ZETSUBOU GAKUEN Manga. The thing is that it doesn't seem to be completed so most likely, that's why tu cannot find the continuation anywhere. So yeah, if tu want to see the whole story, the Game is your best option. tu could also do a research on the DR1 game which is much más detailed compared to the anime and DR: Another Episode - Ultra Despair Girls which takes place between the first two. Pretty much, when it comes to this series, the Games are the main focus !!!!

You're very welcome ^_^ !!!!