That depends on what you are spraying and your intended dispersal area and rate.
Typically where you can find a pulse, but normally on softer skin areas of the body, where your blood supply is the highest, and skin is naturally moistest. These areas are where typically you would find the most natural Pheromones, So added synthetic ones are best applied to these points on your body. Normally this is where a doctor would look for a Pulse; wrists, neck, chest, hips and ears are most common. Armpits, Knees, Ankles and groin are not.
Armpits and groin - to many natural pheromones and bacteria make their own scent there, so additional supply would be wasted. As the bacteria will break down the pheromones into your natural funk pretty quickly.
Knees and Ankles - to low to the ground, not much dispersal area, but might work if you were after very short people, are an overly vigorous dancer and fast on your feet or normally have your feet up where people can smell them (for example, behind your ears).
Wrists, forearms, and backs of the hands, tops of the arm - will disperse faster and further than the neck or chest. These places are easier to get closer to or into a person’s “personal space”, so they will pickup the scent trail better.
tops of the arms are used for faster disbursement. I would usually use social Pheromones in these areas, as sexual ones will draw a much longer range (at a bar or a club this might be the desired effect, in a social or work setting this may cause undesired tension)
Chest - good for close-up intimate pheromones. (often I have had girl or female friend sitting on my lap, laying her head on my shoulder twirling my shirt or chest hair when I sprayed my chest with something good to smell)
Neck - Good for long dispersal wear. will disperse better than the Chest, as it is typically not covered with a shirt. Also remember that the neck is front (Adam’s apple), sides, under the ears, and back or nape. when layering you can add a different phero to each spot.
Ears and behind the ears - similar to the hair, but with better personal pheromone tagging and potentially longer wear down time.
Hair - good for dispersing Pheromones most rapidly, due to the extra surface area provided. Pheromones may last a little longer, but do not get tagged as clearly with your natural scents. These natural tags will help people pick out it is you giving off these pheromones not just a general good feeling or smell for an area.
Clothes similar to hair, and may be good in some locations as heat will make you sweat more and disperse your pheromones faster, Humid areas will cause more sweat to sit on your skin and can help pheromones disperse, but dry areas will be carried out with your sweat you never see as it dries as fast as you produce it. Also clothing application maybe required to wear these in cooler areas where you are wearing more clothing and normally wearing multiple layers of clothes.