Guild Wars 2

I want to know the best build for dungeon…

ah, the “best build” question. Has it ever been answered in any MMO?

Truth is: there is no best build. There are, however, some good builds in the post-your-build-thread: https://forum-en.gw2archive.eu/forum/professions/engineer/Post-Your-Build-Thread/page/3#post1627576

There are definitely some bad builds to avoid. Avoid turrets and gadgets, and avoid spending lots of time auto-attacking with either pistol or rifle. (Rifle isn’t too bad, but pistol auto-attack is horrid)

The best damage comes from grenade kit and bomb kit. For grenades to be good you need the grenadier master trait.

Elixirs are good, rather underwhelming in their support potential (except for R), but there are some good elixir traits that you can swap between as necessary while out of combat.

Only you can decide what is the best build to play, each engineer can have a very different play style and on how they would like to play. What type of support do you want to be? Dps? Healing? Team support? CC master?
Rather asking what is the “best build”, start giving us specifications to how you like to play and then we can start talking ^_______^=

I love playing an all-round build called the sickman syndrome build. In that build I play as a kitmaster that can provide team support, healing, CC and decent dps. I trait it to have good survivabilty and its very adaptable to most pve situation.