É mais que ele tem acesso a todo o conhecimento do mundo.

Embora isso não tenha sido confirmado, é muito provável que Bran realmente não "saiba tudo" no sentido em que todos pensamos, mas ele tenha acesso a tudo o que sabe procurar, aqui está um bom post do Quora explicando isso, mas com ele sem saber sobre o plano de Cersei, em vez dos poderes de Arya.

So for Bran to “see” things (not counting his warging into crows/ravens/animals), he has to know to look for it.

So, 3 Eyes (before Bran) wanted to show Bran the Tower of Joy fight scene and the death of Lyanna. So Bran searched in his Game of Thrones YouTube folder (well technically 3 eyes’ youtube folder) and they watched it. That's why Bran really only thought to say “Hey Jon isn’t Snow, He’s Sand!”. Now if 3 Eye (had planned to before dying) show that Rhegar and Lyanna were actually in a legitimate two sided relationship filled with love and nookie, then Bran would know about Jon being a Targ.

However, Bran didn’t know that and technically didn’t have a reason to even ask since in his mind, and really anyone’s mind that is not privy to the R + L = J theory (they wouldn’t be in story), he probably thinks the key points are Jon is actually a Sand, and Lyanna dyed in child birth. Maybe he Brangoogles who Lyanna had nookie with to make baby Jon, but the wedding in the forrest might not be something he’d actively be looking for.

So unless Bran has a reason to tune into Cersei being a shithead with Euron channel, he won’t. I’m sure someone could ask Bran to, but it doesn’t seem like the characters know the full extent of his powers besides maybe Meera but she’s gone home now.

So like many others, I think Bran can see what he wants, he search to see what he wants, but like me, unless he wants to see a certain scene or whatever, its not just all playing in his head.

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_{If Bran Stark can see everything, why didn't he see Cersei's plan with the Golden Company and the mercenaries? - Quora}

Embora isso não tenha sido confirmado, parece provável, e se assumirmos que é verdade, ele provavelmente não saberia procurar o treinamento de Arya com os homens sem rosto.