In Harry Potter 6 on ds how do you spy malfoy?

You can't spy on Malfoy in Harry Potter and the Half-Blood Prince for the Nintendo DS. There is no specific gameplay mechanic or mission that allows you to do that in the game.

The focus of the game is on Harry's journey as he tries to understand the secrets of Voldemort's past, learn advanced spells, and uncover the identity of the Half-Blood Prince. While Malfoy is a prominent character, the game doesn't involve you in directly spying on his activities.

Perhaps you're thinking of a different Harry Potter game, or a different way to interact with Malfoy in the story?