What documents fall under citizenship documents?

Question

in case of passport application.

Answer 1

Do you mean for Canadian citizens (since you posted in Canada)?  Don't know.  If you mean the US:

Previous U.S. Passport (mutilated, altered, or damaged passports are not acceptable as evidence of U.S. citizenship.)

Certified birth certificate issued by the city, county or state

  Please note that some short (abstract) versions of birth certificates may not be acceptable for passport purposes.

Consular Report of Birth Abroad or Certification of Birth

Naturalization Certificate

Certificate of Citizenship