The Users tab in Device Details gives information about users who have logged into the endpoint. You can reach this tab at: https://my.server.address/devices/<fw_device_id>/users
Normally, we are going to use the users tab to get information about who has logged onto a device. Login count gives a pretty good indication of whom the primary user is (assuming of course that folks do logout/login occasionally).
Note that data will only show where it makes sense for the OS flavor. Below is an example of a simple Windows device: