What is the second command that provides additional data on a user?

The command that provides additional data on a user is "who." This command displays the currently logged-in users along with information such as their terminal, login time, and originating IP address or hostname. This helps in understanding user activity and the system's usage by providing details about who is logged in and their session.

In contrast, while "whoami" shows the username of the currently logged-in user, it does not provide information about other users. The command "w" gives more detailed information including who is logged in and what they are doing, but it is not meant specifically for identifying logged-in users alone. "What" is not a standard command in Linux for this purpose. Thus, "who" is the most appropriate choice for obtaining a list of logged-in users along with relevant details.