[Discussion] I'm not so sure but...

[Byron123]

Well during his old age Madara had the Zetsu as spies so he could have gathered a lot of information from the uchiha clan and even if we assume that he did not, he did have the chance to read the uchiha tablet and since there it says how awake the MS in the first place it would only make sense to explain in detail its abilities.

 

[scorezor]

Tobi is uchiha madara and he knows about izanagi , ofc that he knows about izanami as well U_U.