Obtain a Large Femur from a Skeletal Woodcutter and use it to incapacitate Maloric. Search Maloric for evidence, then report back to Crusader Rhydalla at the Argent Tournament Grounds.
Every day, the Black Knight's squire, Maloric, makes a big show of heading to Crystalsong Forest with his axe over his shoulder. He wants us to believe he's chopping wood, but he never returns with more than a few twigs.
He usually goes toward the ruins southwest of the Mirror of Twilight. He spends a lot of time out there, even for a squire with responsibilities to his knight.
Find a way to distract or incapacitate him and search him. If he's up to something, we'll know it.