وَلَهُۥ مَا سَكَنَ فِى ٱلَّيْلِ وَٱلنَّهَارِ … وَإِن يَمْسَسْكَ ٱللَّهُ بِضُرٍّ فَلَا كَاشِفَ لَهُۥٓ إِلَّا هُوَ · قُلْ أَىُّ شَىْءٍ أَكْبَرُ شَهَٰدَةً قُلِ ٱللَّهُ شَهِيدٌۢ بَيْنِى وَبَيْنَكُمْ
"And to Him belongs whatever rests in the night and the day… And if God touches you with harm, there is none to remove it but He. Say: 'What thing is greatest in testimony?' Say: 'God is witness between me and you.'"
مَا سَكَنَ فِى ٱلَّيْلِ وَٱلنَّهَارِ — the root س-ك-ن was treated at al-Anʿām 6/96 (wa jaʿala'l-layla sakanā) and at al-Fatḥ 48/4. The use here has the sense "everything that lodges, everything that comes to rest".
فَلَا كَاشِفَ لَهُۥٓ إِلَّا هُوَ — kashf (the lifting of the veil): treated at Qāf 50/22 (fa-kashafnā ʿanka ghiṭāʾak).
And it must be recorded that the sentence is built in two directions: for harm, lā kāshifa lahu; for good, fa-huwa ʿalā kulli shayʾin qadīr. Two situations, in two separate expressions.
قُلْ أَىُّ شَىْءٍ أَكْبَرُ شَهَٰدَةً — a question is asked and its answer is given in the same verse: quli'llāh.
I record this as an observation about the word order: two quls (say) come one after the other — one carries the question, the other the answer. No answer from the other side is awaited.
ٱلَّذِينَ ءَاتَيْنَٰهُمُ ٱلْكِتَٰبَ يَعْرِفُونَهُۥ كَمَا يَعْرِفُونَ أَبْنَآءَهُمُ (20) — "they know him as they know their own sons." The same expression was treated at al-Baqara 2/146; I rely on that treatment.
وَمَنْ أَظْلَمُ مِمَّنِ ٱفْتَرَىٰ عَلَى ٱللَّهِ كَذِبًا (21) — this pattern will return several times in the sūra (93, 144, 157). And it is directly connected with the backbone of the sūra: ascribing a prohibition to God.
ٱنظُرْ كَيْفَ كَذَبُوا۟ عَلَىٰٓ أَنفُسِهِمْ (24) — "look how they lied against themselves." The one lied to is given as themselves.