Right now im using a proyectiles rogue but i was wondering how to properly use a dagger rogue? do i really have to be in the back of the monster to backstab or its random chance on the attack?
Also there is any benefit on dual weilding weapons? do you attack with both at the same time, or something?

AFAIK backstab only works from behind not while flanking. And dual wielding would mean klicking one weapon then the other, unless there is a special mechanic for it? Since attacking with one weapon sets a cool down for both hands that won't work.

Maybe its a new feature that will be implemented in the new patches and other things o3o

There is no benefit to having two weapons.
It'd be neat if there was a dual-wielding skill or something, but there's not.

I really, really hope they keep working on Grimrock and expand upon the concepts until we're back to the glory of the genre, reinvigorated.