Job Shadowing is the technique of observing a user at their workplace to understand their activities throughout the day.
If you ask a user what they do during a regular workday, they will give you some insights and you may gain some knowledge about them. If you really want an unedited account of their work day job shadowing is an excellent technique.
As humans we are prone to leave out details when asked and just remember the out of the ordinary events that happen to us. By following the user you get valuable information that would have been lost to the user’s memory.