Quae sciat is an indirect question and works as the subject of the impersonal verb refert. Quae is an interrogative pronoun in the neuter plural, meaning "what things", and is the direct object of sciat.
Quot quisque sit annos natus also is an indirect question, and is the subject of a second implied refert, i.e. it's as if the sentence were non quot quisque sit annos natus refert, sed quae sciat refert, but the refert doesn't actually need to be repeated as it's understood that it applies to both parts. It would be awkward to repeat it. Quot annos is an accusative of duration.
Is there anything else that you're wondering about?