Major objectives.
What value does the system deliver?
What are the major business goals?
What are the most important functions of the system?
What activities or processes does it offer?
Which decisions lead to the current state of the system?
Important technologies used for development and operation.
For whom are we creating value?
Who is paying for development?
Who is paying for operations?
Who are our most important customers?
Who are our most important contributors?
Speed, scalability, reliability, usability, security, safety, capacity or similar.
What are the most important external interfaces or neighboring systems?
Major building blocks of the system.
Potential problems and risks?
What information is missing or has gotten lost?
What is hindering the team from delivering better value faster?