Is it permissible to say "Allah has spoken the truth" after reciting a verse such as: {Indeed, Allah knows, and you do not know}, or does that contravene the Sunnah which stipulated seeking refuge, seeking forgiveness, and glorifying Allah in their appropriate contexts?

There is no harm for the reader or listener to say "Allah has spoken the truth" when passing by His Almighty saying: "And Allah knows, while you do not know," or any other suitable remembrance or supplication. Rather, it is from the Sunnah, as the Prophet, peace and blessings be upon him, used to seek refuge [with Allah] when passing by a verse of seeking refuge. It is also recommended for the reader to ask Allah for mercy when reaching a verse of mercy, to seek refuge when reaching a verse of punishment, to glorify [Allah] when reaching a verse of glorification, to reflect when reaching a verse of parable, and to say what is appropriate when reciting certain specific verses. This indicates the importance of contemplation and reflection on the Quran.