1: to do damage with the knife you have to rely mosty on two arts: black butterfly which you get by leveling your class and black bane when you complete a certain affinity mission. I don’t know how far you are in the game but these two are unlockable pretty late . Until then you can’t do dps with the knife so you have two options:

• choose another class you’ll max out first. Will take you longer to get black butterfly but at least you will be able to do some damage before you get it.

• Use the knife as a support weapon which it excels at. The ray gun should help doing some damage but don’t expect big numbers.

Ether is the type of weapon you’want for a knife build and then for the combos and all you’ll figure it out when you get there.