haqq and haaqqah are 2 different words in arabic
haqq means truth
haqqah is a different form of haqq, in this context it refers to the day of judgement, but the form of the word is changed to emphasise the truth/reality of that day
tafseer maariful quran
This Surah is almost wholly devoted to the subject of inevitability of the Resurrection, its horrors, the punishment of unbelievers and the reward of believers. The Day of Judgment is variously referred to in the Qur'an, and in this Surah we encounter the following three names: الْحَاقَّةُ Al-Haqqah 'Imminent Happening', الْقَارِعَةِ Al-Qari'ah 'Shocking Event' and الْوَاقِعَةُ -waqi` ah 'Happening'.
The word الْحَاقَّةُ Al-haqqah means an 'established fact, or inevitable event, reality or truth'. The word Al-haqqah also means 'Something that provide evidence that something is true.' It can be applied to the Day of Judgment in both senses of the word, because in the first sense the Day of Judgment itself is an established truth, and its occurrence is a certainty. And in the other sense the Day of Judgment will prove to the believers the reality of Paradise and to the unbelievers the reality of Hell. This name of the Day of Judgment is followed by two questions regarding it. The questions have been put to make the readers realise how horrifying the experience would be - beyond normal experience or even imagination.