I know the steinberg vsl 2020 has adat output.But on the the back the adat outputs are these black things,what kind of cable would i need to get to use those adat outputs to the my mixers inputs.
Those "black things" are probably the plugs that are inserted into the Toslink jacks to keep your dust collection from moving in. If you pull one out you'll see a roughly oblong hole that the end of a Toslink optical cable will fit into. I say roughly oblong because they have a chamfered side and a couple of slits to match up with the cable.
At the steinberg website,it says,that each adat out can hold 4 outputs,woyld I ave to get a optical cable to go in one the side where the black things are,and the other sides have inputs,to go in my mixer.