Shamanism is the magic of the Uriash elders. Coen can learn it from glyphs in the Pilgrimage of Power questline. It draws on nature, like fog and lightning, rather than hexes.
Uriash shamans call down lightning, raise fog and can take animal shapes. Coen learns parts of it by finding glyphs and carving them into his own flesh.
Follow the Pilgrimage of Power questline and find the glyphs on stone monuments.