"Heels-up Harris" is my favorite but it would shock me if he said it (wouldn't be the first time).
This one's complicated. He can't point out that she's the real candidate because a) that doesn't translate well into a nick-name: "President Harris?" --yikes! b) he can't reference her slave owning ancestral history: "Kunta Kinte Kamala?" --noppity, nope, nope. c) he can't attack her on her excessive prosecutorial actions: "Hound Dog Harris?" -- he's pro cop.
So he's attacked her as being far, far Left. Which we grok but not so sure the rest of America does. Anyway, so taking that approach: "Komrade Kamala?"
What are others?
That’s because she’s not worthy of a nickname
No point in drawing attention to her and having the DemoKKKrats get more votes from the “I must vote for someone because they are black” group