"They ask, 'When is the Day of Judgment?'" meaning: When is the Day of Judgment? This is done by them as mockery and denial, meaning: It will not happen.
﴿يسْأَلُون أَيَّانَ يَوْم الدّين﴾ أَي: مَتى يَوْم الدّين؟ وَذَلِكَ مِنْهُم استهزاء وَتَكْذيب، أَي: لَا يكون.
