As a tank, Knight relies on his debuffs more than any defensive ability. Power Break cuts a target's damage in half, and reduces attack speed. Speed Break reduces nearby enemies' attack speeds to the minimum. The cooldown of these abilities are equal to the durations, so you can always keep them on the enemies. If fighting multiple enemies, Power Break the stronger one and Speed Break all. If the enemies are the same type, Power Break the one that your team is not focusing.