N-acetyl glucosamine (N-AcG) comes from the outer shell of shellfish. Studies indicate it might help protect the lining of the stomach and intestines. N-AcG seems to be an energy source for friendly organisms within the microbiota, which may account for its protective benefits to the intestinal tract. 
 
There is early evidence that taking N-AcG by mouth or rectally might decrease symptoms of Irritable Bowel Syndrome, Crohn’s disease, or ulcerative colitis, conditions that are known to have deterioration of the gut microbiota. While a holistic practitioner will always focus on reestablishing a healthy microbiota, sometimes we also need therapies and treatments to help with flared symptoms. 
 
Do not confuse N-AcG with the forms of glucosamine that are used in holistic therapies for osteoarthritis; the supplements are very different. For osteoarthritis, glucosamine sulfate is used. N-AcG, since it is derived from shellfish, carries the risk of causing a reaction in individuals who are allergic to shellfish. Also, N-AcG may raise insulin levels, interact with prescription medications, and is not recommended for pregnant or nursing women.
 
The appropriate dose of N-AcG glucosamine depends on several factors, such as age, health issues, current medications, and many other factors. The appropriateness of N-AcG for any individual needs to be determined by a natural medicine practitioner. 

Resources

Rxlist.com  “N-acetyl Glucosamine.” Accessed 3 Apr 2020

J. W. Dennis, I. R. Nabi, and M. Demetriou, “Metabolism, cell surface organization, and disease,” Cell, (2009) 139: 7, 1229–1241, Accessed 2 April 2020

J. K. Nicholson, E. Holmes, J. Kinross et al., “Host-gut microbiota metabolic interactions,” Science. (2012) 336, 1262–1267, Accessed 2 Apr 2020

S. Salvatore, R. Heuschkel, S. Tomlin et al., “A pilot study of N-acetyl glucosamine, a nutritional substrate for glycosaminoglycan synthesis, in paediatric chronic inflammatory bowel disease,” Alimentary Pharmacology & Therapeutics.( 2000) 4: 12, 1567–1579, Accessed 2 April 2020