Hi, according to this site, http://www.guidetoonlineschools.com/degrees/healthcare/public-health
"The master’s degree is required for clinical social work and more advanced public health roles. Online public health master’s degree programs require a core of advanced classes in areas like biostatistics, environmental health, epidemiology, occupational safety, health policy, human nutrition, and immunology. The curriculum contains a mixture of classes in social and behavioral sciences, natural sciences, and management issues. Most programs require a practicum or field work experience in a setting such as a hospital, public health department, or nonprofit."
And, according to this site, http://www.guidetoonlineschools.com/degrees/nursing
"Online master’s degrees in nursing can help current nurses learn advanced clinical or administrative skills, or they can be used by non-nurses to enter the nursing profession. Nurse practitioner programs prepare nurses with advanced skills in midwifery, anesthesiology, or other clinical areas. Other master’s degrees discuss the skills for becoming a nurse manager or a nurse educator."
It looks like each of those sites have lists of schools that offer masters in nursing and masters in public health. Each of those sites also has interviews with people currently working in each of the fields, which could give you more insight as to what their jobs are like.
It could be wise to take a course or more in each subject if you are unsure of which program to choose - that may give you a better idea of which subject you will enjoy studying more. In addition, if you have the opportunity to volunteer with nursing and public health professionals, that could help to give you an idea of which career path you may prefer. Good luck! :)