Minato didn't knew it was Obito.

[Thundergod123]

BUT until he noticed he had marked someone from the past and that one was Obito....

FTG tech allows Minato to tell him who that person is.... And that's why FTG is a bit underrated as well.

 

[The7thHokage]

Kind of obvious, but yeah, agree.

 

[Corgi]

Yeah, we all read 637, too.

 

[Bogard]

He knew the guy above the Juubi was the masked guy he faced(reason why he said "i see, i understand now" or something like this), but apparently didn't know said masked guy was Obito. I say apparently because we got FB's before his attack. I don't know if it was Obito's or Minato's FB. If it was Minato's, it would mean that he did know, but on the other hand if it was the case, why would he ask if he was him while facing him directly?