Well I was scroling into some chapters and then i read the titles of some chapters !

Naruto Manga 397 - The One who Knows the Truth !

Naruto Manga 398 - The Origin of Konoha !

Naruto Manga 399 - The Beginning of Everything

This chapters shows Obito as the one who knows everything about Itachi , Uchiha Clan Massacre and The History of Konoha !

The other character that Knows everything is the one that Obito was impersonating meaning " Madara Uchiha "

This makes sense because Sasuke Questions are : What was Itachi ? Our Clan ? The vilage ? What was the Beginning ?

This is the best forshadowing that Kishi did also he showed both Madara and Obito when Sasuke said about the One That knows everything !

The reason of why Sasuke needs Orochimaru is that he knows that he needs the power of the scroll to become strong enough so that he could make Obito and Madara tell him everything !

Conclusion: - Obito will help Sasuke become stronger with the scroll !
- Sasuke will make Obito and Madara to tell him everything !