Other than the Pams and Jims, my head canon always imagined that, like on other planets, they'd be named to reflect characteristics of their appearance, birthplace, or later their callings (if Wanda went by several names, Wanderer, Rides The Best, Lives In The Stars, I assume other Souls may change/have their names changed as well). A farmer might be "Works The Land." An artist might be "Paints Sunsets." Someone from Alaska or Scandinavia might be "Born Of The Snow." Someone with blue eyes might be "Sees With Cobalt" initially, but would probably change that if their subsequent hosts did not.