ask for it in Sheol below or in the height above

Yahweh uses the words "Sheol" and "height" to mean Ahaz could ask him for anything. (See: rc://en/ta/man/jit/figs-merism)

the height

The abstract noun "height" can be translated with a preposition. "places far above you" (See: rc://en/ta/man/jit/figs-abstractnouns)