Question - "What is the root cause of suffering?"
The rise/presence/existence of this question is exactly the answer to this question.
The minds that doesn't know (presence of ignorance), this question is present/valid/relevant, and suffering exists in them.
The minds that know (void of ignorance), this question is absent/invalid/irrelevant, and suffering doesn't exist in them.
If there's any question arise in the mind, then this mind needs to inquire within, and realizes the answer to any question in the mind, by oneself.
Only the answer/realization that self-realized from within can remove the veil of ignorance in the mind.
Or else, all kinds of information and knowledge that was being learnt, read, heard and accumulated from here and there also cannot remove the veil of ignorance in the mind.
If the mind thinks it has 'the answer' to this question but still perceives suffering, then this mind doesn't really 'know' the answer.