No, Strength/Wisdom is not added to damage rolls
The rules make no mention of ever adding any modifiers to damage rolls, as you've observed; the closest it comes is that using a weapon appropriate to a target's particular vulnerability does a bonus weapon die of damage, as does scoring a critical hit. Hit points and damage numbers in Knave are deliberately a bit flatter than they might be in other comparable systems, since there are no bonuses granted to either hit point rolls or damage rolls, and by default everyone uses the same size hit die (a d8) - so damage bonuses are not necessary to keep up with hit point totals.
Higher level characters who have improved their Strength or Wisdom will still effectively do more damage overall than low level characters, because their increased modifiers mean they are more likely to successfully hit an enemy and get to do damage at all. Also, a higher level character with a better Constitution ability can afford to use more item slots to carry heavier weapons with larger damage dice, while still being able to equip their armour, tools and essential supplies.
This is in keeping with one of the game's stated features:
A PC’s role in the party is determined largely by the equipment they carry.
To be a damage dealing fighter, you need only equip better weapons; to be a tank, wear better armour. Investing in the relevant abilities as you level unlocks your ability to carry better equipment and use that equipment more reliably.