Answer:
The art of the Japanese Ninja (ninjutsu) was a combination of Martial Art with military training (camouflage, stealth, infiltration, etc.), and cutting edge weaponry (including, chemistry, poisons, and explosives). A modern day practitioner would be more authentically following the philosophy and training of the ninja by learning a comprehensive system of Martial Art from a qualified instructor, studying military teachings and tactics (or by being in the military), and researching the most advanced knowledge of weaponry, and other skills that could be applied in the field of combat as well as military espionage.