SPOILERS!!!! I've read the novel, Abel will know because of a slip of the tongue of a commander (he's not yet introduced in the manhwa) and by the time Abel knew who Karas was, Karas already knew who Abel is and that scene was painful
But isn't Abel calling the Prince (Captain Commender) Sakiba
It's a different commander Karas has 4 commanders under him (they will soon be revealed) Abel genuinely doesn't know who Karas is and that's why it led to Abel calling him Captain Commander cuz he thought his rank is higher than commander but lower than the king
How abel is going to learn about prince identity?