Know Thy Enemy. All Witch Hunters gain proficiency in Arcana, which they can use to detect magic with a DC 10 skill check. This does not allow them to identify items, but they can determine which arcane school is present.

Accusation. As a bonus action you can choose a creature that can hear you and Accuse them of heresy, making the creature Hostile towards you. You may not accuse another creature until the effect ends, however if the creature dies or is captured, you may use a bonus action to place Accusation on a different creature. While a creature is accused, you gain advantage for skill checks to uncover information about its whereabouts, any knowledge checks about any capabilities or weaknesses it might have, and any charisma checks against it. While making attack rolls against an Accused creature, you add your proficiency bonus to damage.

Blood Will Out. Your senses are finely honed to the presence of blood magic and dark necromancy. You can detect the active use of either in a 1 mile per character level radius, and have advantage on all rolls to track and find the user of blood magic or dark necromancy. You can sense any spell caster that knows blood magic or dark necromancy within 100 feet. You can sense any target of past blood magic or dark necromancy within 30 feet.