I’m going for W3–>E3–Warlock
Right now, I’m elementalist circle 1 which has only 1 fire magic, so will arde dagger increase my daamge by a lot or just a little?
The fire damage on arde dagger will apply to all hits not just fire related ones.
Every hit including magic missile and skill like hail?
Yes every single hit you do will have it applied.
Every Psychic Pressure tick too?
thank you very much 
Literally all damage you deal, no matter what class you are, will be positively effected by equipping an Arde Dagger.
im still confused, is the damage bonus apply to the skill? or just auto attack hit?
E V E R Y T H I N G .
Just everything that does atleast 1 damage to monsters gets the bonus effect of Arde Dagger.
[EDIT]; Ok I lied, Reflect Shield doesn’t work with Arde.
**
New:
** Just every attack/skill that you cast and does atleast 1 damage to monsters gets the bonus effect of Arde Dagger.