When did Obitio know Naruto was 9 tails Jinchuuriki?

[Lightbringer]

Because he needs to capture them in order. He didn't have Bee yet.

 

[BenjerminGaye]

If he knew it when team 7 fough Tobi (funny prankster Obito) whey didn't he just take him then and there?

If you dont believe Obito could have taken Naruto then think again, watch this video, he could have easily taken Naruto like 4 times.

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Fast forward to 4:10 no explenation needed....

The tailed beasts have to be sealed in order. He doesn't have the means to contain the 9 tails for extended periods.
Tbh naruto wasn't on his radar until the first 7 were sealed.

 

[Zol]

He probably learned about it sometime before the beginning of the series, as the Akatsuki already knew about it when Itachi and Kisame first appeared.

 

[Rogerr]

He knew the second Naruto walked in the room with

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that he had to be the Jinchurriki