I have no formal training in diplomacy but as a mother and grandmother I have learned a few things.
My views on what to do with N Korea may be simple and pollyannish but - here they are.
I would congratulate their leader on the successful test of their nuclear underground test. I would say, "congratulations on becoming a new member of the nuclear fraternity. We all have an obligation to control our emotions and speech. Whatever we say must never be able to be interpreted as a threat to use the tremendous destructive power that we now possess. Let's talk!"