I am confused as to why the "where" in the sentence
One domain where this is of considerable significance is music's potentially damaging effects on the ability to drive safely.
cannot be a "which". Same goes for the sentence
It had long been something of a mystery where, and on what, the northern fur seals of the eastern Pacific feed during the winter, which they spend off the coast of North America from California to Alaska.
Why can't the "which" in the sentence be a "when"?