This guide is taken from sources from the current patch,created to show what works in the current patch and meta for all those ekko manes
why trinity force? well what tank ekko lacked since its Nerf was dmg so the trip force gives you dmg earlier but you aren't that tanky ,so you got to wait it out till your 2nd or 3rd item.
Even though its strange to stick Trinity on ekko it work surprisingly.you stack passive faster ,that's what you do with ekko poke them and use passive to go away in lane constantly herasing with it.