First, fighting hidden hunger simply refers to the fight of micro-nutrient deficiencies, it is called hidden because most of the time it is not perceived until it's too late.
The reason fighting Hidden Hunger is important is because it is a worldwide phenomenon affecting almost 1/3 of the world’s population. The major reason for its occurrence is poverty and poor education, it can be related to poor diet quality and low food diversity. The majority affected are women and young children which leads to an impaired physical and cognitive development in children.
Now, to assess hidden hunger in a community means that you need to assess micro-nutrient deficiencies in this community, you need to identify the markers that you are interested in screening (e.g; Vitamin A, D, Iodine, Hemoglobin,...) before starting your study. If your country started a food fortification program, you might be interested in studying how far the program has helped in fighting the deficiencies.
In addition to the information he gave it is also important to assess the dietary intake of the specific micronutrients of interest. Some specific micronutrients of much global attention at the moment are iron, zinc, vitamin A and iodine. However, you should be informed by the dietary pattens in your target communities so that you address relevant micronutrients. You could consider using either 24 hr recall or quantitative food frequency dietary methodology to estimate the intakes.