I'm building a red/black EDH deck can I put in these cards:
{Obelisk of Jund}
{Obelisk of Grixis}
{Crumbling Necropolis}
{Savage Lands}
If your commander is {R}{B} only, then I'm afraid the answer is none of those cards can be added. They all contain a color symbol that is outside of your deck's color identity, which is not allowed in commander format rules.
RESOLVED
But if you find cards like say the Zendikar fetch lands scence they say the lands type rather then the symbol you can use them