Jax vs Tryndamere

yeah, trynd is all auto attacks and jax can dodge them for a few seconds then stun and burst trynd down.

Can Jax beat tryndamere late game both 6 items or no?

Yes.

Jax's counterstrike will prevent Trynd from doing anything for 3 of the 5 seconds his ult lasts, and Jax's Grandmaster armor buff will usually insure Jax lives for the extra 2 seconds. Which is one of the most favorable fight-circumstance Tryndamere can realistically hope for. If Trynd doesn't have his ult? Jax slaughters him. If Jax just walked up to Trynd so he could leap-strike away once Counterstrike/CC wears off? Trynd is screwed. If Jax used Exhaust after Counterstrike/CC? Trynd is screwed. If we're talking 6 items and Jax decided to grab Hourglass or Guardian Angel? Trynd is screwed. If Jax just went the default build with Omen and Spirit Visage, he'd probably have enough tank to outlast Trynd's 2 seconds of "I really hope I can kill Jax". If he went counter-phys damage specifically with something like Omen and Thornmail on top of Tabi, Trynd is screwed.

The only way Trynd really wins that fight (or Jax looses it) is if Jax completely wastes Counterstrike and winds up fighting Trynd with counterstrike on CD. Even with Leap Strike, Trynd 6-items can still win if he forces Jax to panic and flee (Trynd does not suck at chasing). And with a few seconds being a key factor, if Jax derps-out and ends Counterstrike early for the stun, that counts as wasting Counter-strike.

All that said - Trynd 6-items in is a little bit scarier to fight than Jax 6-items for most champions and probably the stronger late-game champion. Jax is just a massive counterpick to Trynd for the entire game, and he's not far behind Trynd end-game.