How to calculate current density in an Electrolysis Process?
Do I use the total surface area of both Cathode and Anode or just Anode?


You use the cross-section, just like it were a wire.


  Cross-section of both Anode and Cathode or just Anode? 


Just one. Like in a wire, you would measure the cross-sectional area once, not cut the wire into many piece and add up all the areas.