This would be a complete workup of a person's dietary intake, dietary needs, and current physical status. A full assessment would begin with a physical examination that recorded the person's weight, height, and overall physical health. Blood would be drawn and a number of parameters examined, including red blood cell status, blood proteins, and various ions.
Then the person would be interviewed to explore their dietary basics; for instance if they are a vegetarian, or have any food allergies. Then they would be asked to record everything they eat or drink for some set period of time. Dietary intake can then be input into a computer and the diet can be analysed to compare the person's average intake of calories and nutrients to their needs. It's important that this be done as an average - what a person eats in one day is not a fair basis to analyse their diet on. Generally at least a week of records would be needed to make a fair judgement, and longer would be better. There are a number of online services that can be used to assess your own diet, such as www.mypyramid.gov and www.fitday.com.