Typically, there aren't strict professional certifications for this. However, having a background in psychology, sociology, or related fields could be helpful in understanding the emotional and human aspects of end-of-life experiences. Good writing skills and the ability to handle sensitive topics with care are crucial.
To be honest, no particular certifications are compulsory. What matters most is your ability to convey profound emotions and tell touching stories. Maybe some training in narrative writing or experience in similar sensitive genres would give you an edge.