By seeing all of the Pokemon there are in Sinnoh.
No, there is not a Pokedex after the National Pokedex in Pokemon Diamond Version.
you compete the sinnoh dex.
What you have to do is catch all the Pokemon from all the other regions(complete national dex.
In the sinnoh dex,it is Feebas In the national dex,Omanyte
Beat the Champion Cynthia
you cant get every Pokemon be4 you get the national dex
You can get the national dex from the professor after you have seen every Pokemon in sinnoh.
No. It's part of the Sinnoh dex.
In Sinnoh Dex it's unown and in national dex it's tangela.
On your Diamond you have to have the national dex, but in your GBA game you don't.
After you get the National Dex
No but you can in platinum