Explanation
According to the ISACA Cloud Auditing Knowledge Certificate Study Guide, the primary goal of a cloud auditor during the planning phase of a cloud audit is to address audit objectives1. The audit objectives are the specific questions that the audit aims to answer, such as whether the cloud service meets the security, compliance, performance, and availability requirements of the cloud customer. The audit objectives should be aligned with the organization's context, risk appetite, and expectations. The audit objectives should also be clear, measurable, achievable, relevant, and timely.
The other options are not the primary goal of a cloud auditor during the planning phase of a cloud audit.
Option A is a possible activity, but not the main goal of the planning phase. The appropriate tests are determined based on the audit objectives, criteria, and methodology. Option C is a possible constraint, but not the main goal of the planning phase. The audit resources should be allocated based on the audit scope, complexity, and significance. Option D is a possible outcome, but not the main goal of the planning phase.
The sufficient evidence is collected during the execution phase of the audit, based on the audit plan.
References:
ISACA Cloud Auditing Knowledge Certificate Study Guide, page 12-13.

Explanation
The cloud auditor should check if there is explicit documented approval from all customers whose data is affected by the transfer of production data to the test environment. This is because production data may contain sensitive or personal information that is subject to privacy and security regulations, such as the General Data Protection Regulation (GDPR) or the Health Insurance Portability and Accountability Act (HIPAA). Therefore, using production data for testing purposes without the consent of the data owners may violate their rights and expose the organization to legal and reputational risks. This is also stated in the Cloud Controls Matrix (CCM) control DSI-04: Production / Non-Production Environments12, which is part of the Data Security & Information Lifecycle Management domain. The CCM is a cybersecurity control framework for cloud computing that can be used by cloud customers to build an operational cloud risk management program.
The other options are not directly related to the question. Option A, approval of the change by the change advisory board, refers to the process of reviewing and authorizing changes to the system or software before they are implemented in the production environment. This is a good practice for ensuring the quality and reliability of the system or software, but it does not address the issue of using production data for testing purposes. Option C, training for the librarian, refers to the process of providing adequate education and awareness to the staff who are responsible for managing and transferring data between different environments.
This is a good practice for ensuring the competence and accountability of the staff, but it does not address the issue of obtaining consent from the data owners. Option D, verification that the hardware of the test and production environments are compatible, refers to the process of ensuring that the system or software can run smoothly and consistently on both environments. This is a good practice for ensuring the performance and functionality of the system or software, but it does not address the issue of protecting the privacy and security of the production data. References := Certificate of Cloud Auditing Knowledge (CCAK) Study Guide, Chapter 6: Cloud Security Controls Cloud Controls Matrix (CCM) - CSA3 DSI-04: Production / Non-Production Environments - CSF Tools - Identity Digital1 DSI: Data Security & Information Lifecycle Management - CSF Tools - Identity Digital