أَنَّى لَهُمُ الذِّكْرَى
How could admonition come to them now?
Istibʿād represents an event as unlikely or remote. In annā lahumu al-dhikrā, the question is not a genuine request for a location or source of admonition. The surrounding context points to the remoteness of taking heed after the signs were already rejected.
Annā can ordinarily ask how or whence, but here it conveys the improbability of the claimed awakening. That shift illustrates a transferred rhetorical sense.