What is the best oil for a hot oil treatment? Extra Virgin Olive Oil, Coconut oil, Kemi Oyl
How often should they be done? You can do them as often as once a week, depending on how dry your hair is
How do you know if you need one? If your hair is dry (sometimes). I usually do a hot oil treatment every 3-4 weeks only because of my hair type, sometimes it's moisturized, sometimes it's not.
There could be other factors as to why your hair is dry (if that's the case) and you may need a reconstructor treatment or just deep condish with ORS Hair Mayo once a week