Based on the understanding of follow-up audits, especially in the context of Information Security Management Systems (ISMS) and the guidelines provided by ISO 19011:2018, here are the four questions from your list that the auditor in training has answered correctly:
B). Q: Should follow-up audits seek to ensure nonconformities have been effectively addressed? A: YES This is correct. The primary purpose of follow-up audits is to verify that nonconformities identified in previous audits have been effectively addressed and the corrective actions taken are suitable and effective.
D). Q: Is the purpose of a follow-up audit to verify the completion of corrections, corrective actions, and opportunities for improvement? A: YES Yes, the follow-up audit aims to verify the completion and effectiveness of corrections and corrective actions. It may also consider the implementation of opportunities for improvement identified during the initial audit.
E). Q: Are follow-up audits required for all audits? A: NO This is correct. Follow-up audits are not automatically required for all audits. They are typically conducted when nonconformities or other significant issues were identified in an earlier audit and there's a need to verify the implementation and effectiveness of the corrective actions.
H). Q: Could an outcome from a follow-up audit be another follow-up audit if required? A: YES Yes, this is a possible outcome. If the follow-up audit finds that the corrective actions have not been fully effective, or if new issues are identified, it may be necessary to conduct another follow-up audit.
The other responses provided by the auditor in training require some clarification or correction. For instance, while a follow-up audit primarily focuses on previously identified nonconformities and corrective actions, it can still identify new nonconformities if observed (A). Opportunities for improvement are generally considered in the scope of regular audits more so than in follow-up audits, which are more narrowly focused on corrective actions (C). Also, the outcomes of follow-up audits should typically be reported to both the audit team leader and the audit client (F and G), ensuring transparency and accountability.
The four questions that the auditor in training has answered correctly are B, D, E, and H. These questions and answers are consistent with the definition and purpose of a follow-up audit as specified in ISO 19011:2018, Clause 6.712. A follow-up audit is conducted to verify the completion and effectiveness of corrective actions taken as a result of a previous audit (B, D). Follow-up audits are not mandatory for all audits, but they may be required by the audit program, the audit client, or other interested parties (E). The outcome of a follow-up audit may be another follow-up audit if the corrective actions are not satisfactory or not completed within the agreed time frame (H). The other questions and answers are either incorrect or irrelevant. A follow-up audit should not seek to identify new nonconformities, as this is not its objective (A). Follow-up audits should consider agreed opportunities for improvement as well as corrective actions, as they are both outputs of a previous audit . The outcome of a follow-up audit should be reported to the audit client, as well as to other relevant parties, such as the audit team leader who carried out the previous audit (F, G). References: 1: ISO 19011:2018, Guidelines for auditing management systems, Clause 6.7 \n2: PECB Certified ISO/IEC 27001 Lead Auditor Exam Preparation Guide, Domain 6: Closing an ISO/IEC 27001 audit

ISO/IEC 27001 requires organizations to comply with applicable legal, statutory, regulatory, and contractual requirements, including those pertaining to information security. These requirements must be identified, documented, and kept up to date as part of the organization's ISMS.
References: ISO/IEC 27001:2013 Standard, Clause 6.1.3 (Information security requirements)

Explanation
A checklist is a tool that helps auditors to collect and verify information relevant to the audit objectives and scope. It can provide the following advantages:
Ensuring relevant audit trails are followed: A checklist can help auditors to identify and trace the sources of evidence that support the conformity or nonconformity of the audited criteria. It can also help auditors to avoid missing or overlooking any important aspects of the audit.
Ensuring the audit plan is implemented: A checklist can help auditors to follow and fulfil the audit plan, which describes the arrangements and details of the audit, such as the objectives, scope, criteria, schedule, roles, and responsibilities. It can also help auditors to manage their time and resources effectively and efficiently.
The other options are not advantages of using a checklist, but rather:
Using the same checklist for every audit without review: This is a disadvantage of using a checklist, as it can lead to a rigid and ineffective audit approach. A checklist should be tailored and adapted to each specific audit, taking into account the context, risks, and changes of the auditee and the audit criteria. A checklist should also be reviewed and updated periodically to ensure its validity and relevance.
Restricting interviews to nominated parties: This is a disadvantage of using a checklist, as it can limit the scope and depth of the audit. A checklist should not prevent auditors from interviewing other relevant parties or sources of information that may provide valuable evidence or insights for the audit. A checklist should be used as a guide, not as a constraint.
Reducing audit duration: This is not necessarily an advantage of using a checklist, as it depends on various factors, such as the complexity, size, and maturity of the auditee's ISMS, the availability and quality of evidence, the competence and experience of the auditors, and the level of cooperation and communication between the auditors and the auditee. A checklist may help reduce audit duration by improving efficiency and organization, but it may also increase audit duration by requiring more evidence or verification.
Not varying from the checklist when necessary: This is a disadvantage of using a checklist, as it can result in a superficial or incomplete audit. A checklist should not prevent auditors from exploring or investigating any issues or concerns that arise during the audit, even if they are not included in the checklist. A checklist should be used as a support, not as a substitute.
References:
ISO/IEC 27001:2022 Lead Auditor (Information Security Management Systems) objectives and content from Quality.org and PECB ISO 19011:2018 Guidelines for auditing management systems [Section 6.2.2]

Explanation:
A third-party audit is an independent assessment of an organisation's management system by an external auditor, who is not affiliated with the organisation or its customers. The auditor verifies that the management system meets the requirements of a specific standard, such as ISO 27001, and evaluates its effectiveness and performance. The auditor also identifies any strengths, weaknesses, opportunities, or risks of the management system, and provides recommendations for improvement. The purpose of a third-party audit is to provide an objective and impartial evaluation of the organisation's management system, and to inform a certification decision by a certification body. A certification body is an organisation that grants a certificate of conformity to the organisation, after reviewing the audit report and evidence, and confirming that the management system meets the certification criteria. A certification decision is the outcome of the certification process, which can be positive (granting, maintaining, renewing, or expanding the scope of certification) or negative (suspending, withdrawing, or reducing the scope of certification). References:
* PECB Candidate Handbook ISO 27001 Lead Auditor, pages 19-25
* ISO 19011:2018 - Guidelines for auditing management systems
* The ISO 27001 audit process | ISMS.online