
https://blessedempyrean.wordpress.com/sidekick-prince/
happy reading!

It's a bit tough since the manhwa is paced faster than the novel but roughly, the chapters currently are:
(Manhwa) Chapters 9-10 coincides with Chapters 16-19 in the novel
(Confrontation with Maximo 2, Renato proposes contract marriage to Khalid)
(Manhwa) Chapters 11-12 coincides with Chapters 20-25 in the novel
(Starting from Khalid rejecting the contract, Snake's Breath, Banquet and dog running towards Renato)
If you have the time I'd advice to at least start from chapter 10 in the novel to not miss out on any details but chapter 25 is also a good starting point for manhwa readers.
Novel link please and thank you