I wish Trump would tell our military to shoot down any missile launched by NK that leaves their airspace.
In the meantime it would be a good idea if we tried to recover one of those missiles. If possible. Study it.
On the plus side, shooting down NK missiles would serve as a good operational test of our system. After all, the target missiles we shoot at are expensive, so if NK provides the targets, that's a cost savings. It would also demonstrate to our enemies that our system works. This could serve as a very real deterrent to them to try anything if they are convinced it will not work.
On the down side, our interceptors are expensive and limited in inventory. Do we really want to expend them if we may need them to shoot down missiles aimed at someplace we actually care about other than empty ocean? Also, shooting down another Country's vehicle in international airspace/space is technically an act of war. Do we want to give NK diplomatic cover and some modicum of international sympathy?
Me? I'd track their shots with every sensor we have, radar, IR, optical... Eavesdrop on all the telemetry coming off the missile. I'd only shoot if the NK missile was a danger to a populated area.