quotiens

Quotiens does two jobs from one form. As an interrogative it asks "how many times", direct or indirect; as a relative conjunction it means "as often as, whenever", and its correlative is totiens, "so many times". Both are built on quot, "how many", with the numeral-adverb ending you also see in semel, bis, ter and decies.

The spelling is the practical point. Classical texts have quotiens, but the n before s was weak and later manuscripts routinely write quoties; the same happens to totiens and toties. They are one word. In an indirect question quotiens takes the subjunctive, nescio quotiens fecerit, while as a plain relative it takes the indicative. English has no derivative worth the name, which is why translators reach for "how often" and "whenever" and leave it there.