Well, without having read the 'i am the king novel', it's hard to say precisely. But it could center around a person's journey to claim or prove that he is the king. Maybe it involves battles, both physical and mental, against those who oppose his claim. It could also explore themes like leadership, loyalty, and the price of power.
I'm not sure specifically as there could be many novels with this title. It might be about a character who believes he is a king, perhaps in a fictional world filled with power struggles, political intrigue and adventure.