Which document in SAP Ariba collects all customer settings?

The Business Requirement Workbook is the correct choice because it serves as a comprehensive document that collects all customer settings in SAP Ariba. This workbook plays a critical role during the implementation process as it details the specific business requirements, configurations, and settings that need to be addressed to tailor the SAP Ariba solutions to fit the customer's needs. It provides insights into the workflows, processes, and data that are unique to that particular customer, ensuring that the configurations align with their operational requirements.

In contrast, other options such as the Settings Overview Document, Configuration Manual, and Customer Settings Guide, while they may contain useful information regarding settings and configurations, do not encapsulate the entirety of customer-specific requirements and configurations like the Business Requirement Workbook does. These other documents may serve specific purposes or focus on certain aspects but lack the comprehensive overview provided by the workbook.