Regarding world content you’re very unlikely going to be running AOE traits so aslong as you maintain dots, you should be ok. Fan of knives is only worth using when its 3+ targets. you use two mutilate on two targets or less.
Rogue is a squishy class so if you’re struggling, its normal. The default set up for assa rogue should be good for World PVE content. Elaborate planning, subterfuge, vigor, cheatdeath, toxic blade, prey on the weak or internal bleeding (your choice) and lastly poison bomb to save more combo points to dump into Envenom instead of an aoe dot.
If you get the opener in said PVE scenario, you want to apply garrote to as many targets as possible. then work on applying rupture, dump envenoms and just try to maintain dots in between.
Regarding dungeons however. There is a crit build and a mastery build if im not mistaken, for the crit set up you need the echoing blades trait which increases the damage done of your fan of knives, this will replace you using mutilate on must pulls in dungeons. Applying dots remains as normal but this emphasizes heavily on your damage coming from fan of knives (ideally you want to three stack this trait for maximum damage, same again for the shrouded suffocation trait if you decide to go the mastery route.).
As said there is a mastery version which involves you speccing into shrouded suffocation it involves alot more micromanagement as you’re focusing mainly on maintaining and spreading dots.
Talents for echoing blades would be something like this - elaborate planning, master assassin, vigor, cheat death, toxic blade, ironwire, poison bomb.
Talents for shrouded suffocaiton - elaborate planning, subterfuge, vigor, cheat death, toxic blade, ironwire, poison bomb.