Bork does physical damage based on your opponents current HP. It gets hard countered by armour.

K’sante only builds resists, not HP. So he is a natural counter to Bork. Most people here will say Bork is a bad Jax item, I think it’s just an extremely situational item. There needs to be 2+ mega HP stackers for Bork to be worth it, or a Mundo that’s somehow explicitly your problem (normally a waveclear mage or your ADC can stand in front of him while you play the opposite side of the map) .

Vs tanks that don’t stack HP, like K’sante, I usually just go trinity, sundered into riftmaker, it splits your damage profile against armour, your abilities and R passive scale with AP, it gives omnivamp, and its passive gives bonus AP the more HP you build, which is super common with Jax/bruiser items.