A new app builder on the Cloud Kicks team is getting familiar with the data...

The correct answer is C. Schema Builder.

Schema Builder is designed to help app builders visualize the Salesforce data model, including standard objects, custom objects, fields, and relationships. Salesforce Trailhead states that Schema Builder lets users visualize and edit the data model and is useful for understanding complex data models.

Object Manager and Fields & Relationships are used to configure individual objects and fields, but they do not provide the same visual relationship map. Lightning App Builder is for page layout and UI configuration, not data-model visualization.