Kind of vague. He can worship Desna just find...but his magic is bestowed by spirits not gods, so any work. If the player trying to be inspired by desna with spirits then perhaps heavens, maybe as a stretch ancestors.
A shaman worshiping a deity does not really fit. They are based on different belief system that has nothing to do with deities in the traditional sense. Even if they view a deity as extremely powerful spirt they would be unlikely to worship a single deity. They take a more pantheistic approach and would honor all deities. The idea of worshiping a single deity is more a western idea with its emphasis on monotheistic religions.
Based on her portfolio, I'd suggest emphasising the Heavens, Lore, and Wind spirits. I wouldn't outright ban any of them. Slums might work as well, as it fits the trickery portfolio a bit but I'm not entirely sold on it.
A shaman, just like anyone else (aside for clerics, for the most part) can venerate and worship any god they want, even one especially, and still get their powers and abilities from other sources.
A shaman, just like anyone else (aside for clerics, for the most part) can venerate and worship any god they want, even one especially, and still get their powers and abilities from other sources.
Extending this line of thinking, just like Desna won't tell a fighter who worships her "no, don't use a polearm, use a starknife", Desna really doesn't care what spirits shamans who happen to worship her bond with.
People who don't have their powers come from gods usually aren't held accountable by gods.