So far there have been two nuclear strikes against populous areas world wide, those being Hiroshima and Nagasaki. Since then, while tests and threats have been somewhat common, there has never been a nuclear attack. As such there has never been any reactive need to discuss punitive damages against a state or entity that is found to be responsible for a nuclear attack. MAD pretty well assured during the cold war that the US and Russia kept their fingers of the big red button, and the world has been (Relatively) peaceful since the fall of the soviet union.
That being said, there are now at least two entities that are actively seeking nuclear armaments for the purposes of war. The Islamic State has stated it can buy nuclear weapons from Pakistan (dubious that any nuclear armed nation would be willing to sell their armaments) and North Korea has stated several times in the past month that it could "Destroy US Cities in a just ball of righteous fury" (slightly paraphrased). Neither of these entities seem to be willing to play nicely with the rest of the international community. Not to say it's likely, but has there ever been any discussion of what punitive damages can be taken against a country or entity that is responsible for a nuclear attack?