In zou,kinemon and the other scabbards clearly told the strawhats that Wano is occupied by the pirate emperor Kaido which already highlights they are familiar with the "Emperor" term.
The person in this chapter is telling the whole alliance to not doubt themselves and feel confident for the upcoming war with Brook highlighting the samurai's determination just before that speech.I don't think it is Jinbe,he has no authority to speak to the whole alliance that way.
Let's wait for the Viz version for clarification though.
He’s mentioned the title, but that doesn’t mean he’s intimately familiar with the system itself and the overall threat of one. He knows Kaido, that’s really it. And the Kaido that Kinemon knows is from 20 years ago, not the monster they see now. The speech as stated gives the impression that the speaker very well knows the threat of the title, and that each one is elite. They didn’t say “be proud that we’ve challenged Kaido,” they says “Yonko”. Jinbe worked under two of them and knows their strength and the strength of the other two, having seen it up close. Kinemon wouldn’t know that like Jinbe would, which is why it wouldn’t really sound right to me if it was him.
Authority has nothing to do with it. Jinbe, by virtues of being in Luffy’s crew, has just as much authority in the alliance as anyone else.
It's Brook giving the Yonko speech.
I don’t think so...it doesn’t sound like something he’d say. It sounds like what Jinbe said on WCI, and more like something he’d say in general.