This is a great question. When you are researching any topic, there are a number of theories that you can use. In fact, there are so many theories out there, in all honesty, no one is able to master them all. Theories allow a person to study a topic from different perspectives, which can produce insightful ideas. One social theory that might help is the sociology of knowledge. Let me explain.
The sociology of knowledge states that all knowledge is socially constructed. In other words, each society has its own commonsense view of the world, or we can say that each society has its own cultural idiom of what is right and wrong. So, some cultures might be against the idea of euthanasia, but other cultures might see this as noble. This is the same with suicide. In many cultures suicide is noble and honorable. For example, traditional Japanese culture has room for suicide.
In light of these points, it might be interesting to study euthanasia from a cross cultural point of view. In other words, why do certain cultures oppose it and other culture embrace it?
Also it might be interesting to look at euthanasia from a diachronic point of view. In other words, how did people from different times view euthanasia? The sociology of knowledge can be used here as well.
case study and FGD of persons who want to euthanasia or committed euthanasia. review of secondary data and you should get emotions management methods.