"Jinzo" cannot negate Trap Cards while "Skill Drain" is already active, because "Skill Drain" is negating "Jinzo"'s effect. But if "Jinzo" is already on the field, you cannot activate "Skill Drain" because "Jinzo"'s effect prevents you from doing so.
si cette carte est déjà sur le Terrain, alors l'effet de Jinzo est annulé