I need help with knight's build

[Sarin]

Speaking about agi and vit...

PvM, your build is likely to be STR>AGI>VIT+DEX, essentially a mobber for BB/brandish.
PvP, LK is most used as tank/statuser, that is low STR, high VIT, AGI, DEX. You can alos be a secondary damager/empbreaker, in that case it's a balance of STR, VIT, AGI with quite low dex.

So in fact, there is no real full AGI/full VIT good build, it's how you balance out these stats.