I've read 'Emperor' by Conn Iggulden a few times now, and from what I can tell, it's a standalone novel. It covers a specific arc of Genghis Khan's life, ending in a way that feels complete to me. The author has written plenty of other historical fiction series, but 'Emperor' itself doesn't continue directly. I remember finishing it and feeling a bit sad there wasn't more, but then I started his 'Conqueror' series, which is about the Mongol Empire but features different central figures. It's kind of a spiritual follow-up, I guess, but not a sequel.
If you loved the writing style and the brutal, epic sweep of 'Emperor', checking out 'Conqueror' is probably your next move. The reading order for Iggulden's work can get confusing because he revisits similar eras. For pure Mongol content, 'Wolf of the Plains' (the first 'Conqueror' book) is where I went, and it scratches a similar itch, though it focuses on Genghis from a younger age.