Which of the following sources would provide the most relevant information for the engagement planning process?

Interviews performed with audit client employees are a crucial source of information for the engagement planning process because they provide direct insights into the organization's operations, risks, and internal controls. Engaging with employees allows auditors to gather qualitative data that reflects the actual working environment, processes, and potential areas of concern. This firsthand information can help auditors understand the client’s specific context, culture, and practices, enabling them to tailor the audit approach effectively and address the unique challenges posed by the engagement.

While other sources, such as industry benchmarks, previous audit reports, and regulatory guidelines, can offer valuable context and frameworks for the audit, they may not capture the immediate and practical realities of the client's environment as well as direct employee interviews do. Consequently, leveraging insights from those who are directly involved in the processes being audited enhances the relevance and effectiveness of the audit planning process.