Is it obligatory to repeat the prayers that were performed while wearing a skirt made of wool with a small hole, which is suspected of revealing what is beneath it?

If by small holes, the questioner means the openings within the fabric, then the ruling on prayer in such garments depends on the extent to which the skin is visible. If the skin is visible without close inspection, then the prayer is invalid. However, if it is not visible except upon close inspection, then the prayer is valid.

As for the intent being a single, very small tear, then what is uncovered of the awrah (private parts) is considered very little, and the uncovering of a small amount of the awrah in prayer is excused by the majority of scholars, including the Hanbalis and Abu Hanifa. This is also the chosen view of Sheikh al-Islam Ibn Taymiyyah. The estimation for "a small amount of the awrah" is what is considered small customarily, or what is the size of the little finger.

Based on this, the questioner is not required to repeat the aforementioned prayers as long as what was uncovered was minimal. Some scholars hold the view that the prayer of one who prayed with their awrah uncovered, unknowingly, is valid, though the Malikis recommend repeating it within the time [of the prayer].