The determination of information needs is of course intrinsically linked with information behaviours. Understanding information needs is also a critical success factor in developing and then enhancing intranets and other information services. A good place to start is the book Information Needs Analysis – Principles and practice in information organizations by Daniel G. Dorner, G. E. Gorman and Philip J. Calvert, published in 2014.Another good book on the topic is Looking for Information: A Survey of Research on Information Seeking, Needs and Behavior by Donald Case. However this was originally written in 2002 and in my opinion the updating to the current third edition has not been as thorough as it might have been. Nevertheless this is a very good introduction to the topic, and as a US-published book complements the book by Daniel Dorner et al which was published in the UK.
If you search on a site like Google Scholar you will find that most of the research papers focus on the information needs of patients in a healthcare situation, which can be of significant importance in the speed of recovery. Comparatively few case studies have been published, which is why the books referred to above are so valuable. As illustrations of the processes there are open access papers on the determination of the information needs of Software engineers and in a large US hospital. Even though the hospital case study is primarily about the use of library resources the methodology is more widely applicable.