In chapter 14 of Half-Blood Prince, Harry casts Episkey:
"I can fix that," said Harry, landing beside the two girls, pointing his wand at Demelza’s mouth, and saying "Episkey."
Despite this, chapter 2 of Deathly Hallows shows Harry apparently believing that he doesn't know how to heal wounds:
but he had to admit to himself that this jagged cut in his finger would have defeated him. He had never learned how to repair wounds
Is there an explanation for this apparent contradiction?
Episkey only heals certain kinds of injuries, as described in the Harry Potter Wiki:
Episkey was the incantation of a healing charm that healed relatively minor injuries such as broken noses, toes, and split lips.
The common factor here would appear to be blunt trauma.
Compare the definition of "wound" from the Cambridge Online Dictionary:
to damage an area of the body, especially by making a cut or hole in the skin
[emphasis mine]
So there is no contradiction; Harry knows only the one healing spell, and it doesn't work on wounds.
