The correct answers are D and F .
A second-party audit is an external audit carried out by an organization that has an interest in the auditee, such as a customer auditing a supplier , or by another party acting on that customer’s behalf.
Therefore:
C. An auditor from a customer — participates
This is the clearest example of a second-party audit.
A. An auditor employed by an external consultancy organisation — may participate
A consultancy auditor may conduct the audit on behalf of the customer or interested party, so this can still be a second-party audit.
B. An auditor certified by an auditor certification body — may participate
Auditor certification is a competence credential. It does not determine whether the audit is first-party, second-party, or third-party.
E. An auditor trained in the CQI and IRCA scheme — may participate
Training or qualification does not define the audit type. Such an auditor may participate in a second-party audit if acting for the customer or interested party.
D. A certification body auditor — does not participate in a second-party audit
A certification body auditor performs third-party audits , such as ISO 14001 certification audits.
F. An auditor from an accreditation body — does not participate in a second-party audit
An accreditation body auditor assesses certification bodies, not suppliers or organizations as part of a customer-related second-party audit.
So, the two roles that do not participate in a second-party ISO 14001 audit are D. Certification body auditor and F. Auditor from an accreditation body .