I doubt that.
USA is entangled in two wars and needs Pakistan. Taking out Pakistani nuclear weapons would lead to war between Pakistan and USA.
Even if USA can take out Pakistani nuclear weapons, they won't.
it is True that USA is Engaged in two wars , but as the conditions are going they will be pulling out shortly, And also it is not necessary that they will go against Pakistani nukes them selves , there are far too many forces in the world who don't want to see a Nuclear Pakistan , they will be more then Happy to Act on the Intelligence provided by USA. so if USA knows about it then it would have been over.