The Problem of Criterion

I ran across this ancient problem while reading through my epistemology textbook the other day:

In order to find out what we know, we also have to find out how we know. But in order to find out how we know, we have to find out what we know.

So this problem boils down to two questions:

i) How do we know?
ii) What do we know?

Which one do we answer first?