﴿ وَمَآ أَدْرَىٰكَ مَا ٱلْقَارِعَةُ ﴾

“And what could make thee conceive what that sudden calamity will be?”

And what will show you what will make known to you what the Clattering Blow is? — additional emphasis of its awesomeness the first mā is a subject and what follows it is its predicate; the second mā and its predicate also function together as the second direct object of the verb adrā ‘show’.