Is she asking... what 'how much' means, or how much of... probably the latter. He points at a clock- but it lacks a second hand, it's probably not immediately obvious that it's a timekeeping device. And... in a world without sleep, would they even have a concept of time measured in intervals longer than, say, a minutes-equivalent? Vexing.

"How much does she know numbers? I taught her up through three... but if she knows more, we could mention that your kids have some number of years, and that we have a larger number of years, and see if she picks up on the pattern."