Which of the following actions falls under "Know your Customer"?

The action that best aligns with "Know your Customer" is related to understanding the quantity of alcohol they order. This is important because it assists in assessing the customer's consumption patterns and helps staff identify any potential signs of overconsumption or unsafe behavior. By monitoring how much alcohol a customer orders, establishments can ensure responsible service and compliance with legal regulations regarding alcohol consumption.

In contrast, while understanding where a customer lives, the number of colleagues they brought, or the brands they prefer can provide additional context about a customer, these aspects do not directly relate to the core principle of responsible alcohol service. Knowing the quantity ordered has a more immediate impact on managing service levels and preventing issues related to over-serving or underage drinking.