My car was leaking oil, and its fixed now, but im not sure what i can use to degrease/clean this

 

That looks like its in an area that will never be seen? I would just leave it alone.

 

I would too, but when i use the car alot i can see smoke coming from there, (theres no oil in the valve covers nor rings)

 

I guess spray it down with some degreaser. Then rinse it off with water. It might smoke a little more but will eventually dry up and stop.

 

First thing is to take a rag and wipe off as much as you possibly can without any degreaser, once you have the vast majority cleaned up hit it with some solvent or dishwashing soap then spray it off with water however,

DO NOT SPRAY WATER ON ANY ELECTRONICS.

As for the smoke, unless it's still leaking oil from something it will cook off after a couple drives.