Unfortunately, there is no "One Piece" chapter this week so fans will have to endure a few days before they find out what happens in the Minks' flashback with Jack.
Jack is a curious character, and although he seems overly confident about himself, it seems he is justifiably strong. Many fans are speculating that Jack is Axe-Hand Morgan. Morgan is one of the first marines Luffy ever faced and defeated in battle.
It's unlikely that Morgan is Jack. Morgan was much too weak and no time skip would make him as strong as a Yonkou's right-hand man. It wouldn't be fair to the Strawhats, who became strong during the Timeskip, but not upper-tier level.
In chapter 809, we saw the King of Night, Duke Nekomamushi who protects the Whale Forest. Unlike Duke Inuarashi, Duke Nekomamushi seldom said any words before he unleashed a vicious attack on Jack. The attack was enough to coerce Jack into transforming into his human form.
With that being said, it is likely that we will finally see what Jack looks like. It has already been said in the story's present time that Jack will defeat the Minks using Caesar Clown's poison gas weapon. Will we see it in chapter 810?
What we will see in chapter 810 is some present-time dialogue between Trafalgar Law and Duke Nekomamushi. It would only make sense considering that the story jumped between flashback and present-story when the Strawhats conversed with Duke Inuarashi. Now that Law will meet Duke Nekomamushi, we will also learn what he's plotting.
The crews of Luffy's and Law's both have the mutual drive to defeat Kaido. Still, considering Duke Inuarashi and Duke Nekomamushi's current vendetta, it wouldn't be a surprise if we saw the two crews and two halves of Minks engage in some kind of fight.