Show a structured approach: week one for setup and reading, week two for small contributions. Mention improving the onboarding process for future joiners.
Good answers include: reading documentation and architecture diagrams, tracing a request end-to-end, picking up small bugs to learn the codebase, asking questions without hesitation, setting up the development environment properly, and identifying key people to learn from. Best candidates also mention contributing to onboarding docs for the next person.
Tests humility and learning approach. Strong candidates are comfortable saying "I do not know" and asking questions early. Red flag: claiming they would be productive immediately on any codebase.