The Golden Fool - Robin Hobb (Book 2 in the Tawny Man Trilogy)

Fitz has been persuaded back to court, posing as a servant to the decadent Lord Golden (who is the Fool in disguise).

In secret, he will train Prince Dutiful in the magic known as the Skill. The peace remains fragile, so the diplomatic wedding between Dutiful and the Outislander princess is a crucial alliance. But when Elliania arrives she challenges the prince to undertake an impossible quest before she will accept him.

He must kill Icefyre, one of the last true dragons. And Fitz and the Fool must go with him…