So as far as we know, Blackbeard can’t read Poneglyphs. As we saw with Big Mom and Kaido, they need someone to read the Poneglyphs and they mentioned Nico Robin and Pudding.
So if Kaido knows about Pudding it isn’t out of the question for Blackbeard to know about her too.
Last time we’ve saw Blackbeard, he said he’s going to get something.
I think Blackbeard is going to Whole Cake Island to kidnap Pudding:
- He knows Big Mom is in Wano with Kaido, so she won’t be in Whole Cake Island.
- He will get her Road Poneglyph, as far as we know he needs it too and now is the perfect chance.
- He will probably defeat/kill Katakuri easily, who Luffy was struggling to beat for hours. This might serve as Oda demonstrating Blackbeard’s power compared to Luffy’s.
- He will kidnap Pudding for her to read them for him.
Blackbeard might know how to awaken her eye forcefully. He studies history after all.