I read this manga years ago and I can’t find it or its name. All I remember is that the main character’s master was a dragon that can also has a human form. During one of the chapters main character shaves off a horn of his master to sell it for money.
Could it be 4 Cut Hero
The chapter you mention it is chapter 39. He cut his master horn once and now he do it again.
His master is a dragon and can turn to any human form.