In the book, they never make it clear who the target is. In the show, Daemon clearly says to kill Aemond, and cheese asks what if they can't find him, and you never hear Daemon's answers. In the book, Daemon is in the Riverlands when he hears about Lucerys being killed and just sends Rhenyra a raven that says 'a son for a son'. Then it says he goes and finds Blood and Cheese and sends them niggas on the mission. But it's never explicitly stated who the actual target is. Some say it was one of Alicent's sons who was the intended target - Aegon or Aemond. Some say it was one of Aegon's sons who was the intended target, like in the show.
That's the great thing about the Fire and Blood: It's a book from INSIDE the Game of Thrones universe. It's the book that the Maesters wrote about the Targaryen civil war. And they used eyewitness accounts and records to piece the story together. They tell you in the book basically 'Some of this shit can't really be confirmed or corroborated, and at least some of it we know was told by a nigga who couldn't have possibly been there for all these events. But this is as accurate a history as we can muster.'
So when you're making a show based on it, you really have a lot of stuff to play with because so little if it was set in stone to begin with.
If that makes sense.