Kí ló jẹ́ afihan-an lẹ́tà àtọ́ka?

This question is loosely worded, but it is asking for something in Yoruba speech that people habitually point to or refer back to when making an argument, described here as an àtọ́ka (a pointer or reference). In Yoruba oral tradition, that role belongs to àwọn òwe, proverbs.

Yoruba speech leans heavily on proverbs as ready-made points of reference: a speaker cites a proverb the way a writer cites a source, to point to accepted wisdom and strengthen an argument. This function is captured in the well known saying that a proverb is the horse used to trace and recover a lost line of speech.

Application, complex sentence structure, and machinery do not serve this referencing function in everyday speech, while proverbs are specifically kept and reused as fixed points that a speaker points back to; that is why proverbs are the best fit here, even though the question's phrasing is not fully precise.