Ok as said before Faora in the episode bloodline said to Davis that he looked exactly as his Father "Zod". With that said in that episode u can put 2 and 2 together and get a real picture of how Zod looks in the Smallville Universe. Zod looks exactly as Davis but with a goatee. Now u ask how can Davis be Zod if he is Doomsday? well thats true Davis is Doomsday but that does not mean that Sam Witwer cant play Zod. one of 3 things can happen with Davis:
1. Doomsday takes complete control of Davis and Davis ceases to exist
2. Some one uses Black K on Davis to separate Davis from Doomsday and succeeds but Doomsday kills Davis after they are separated.
3. Davis gets separated from Doomsday as said in the above statement but Zod takes control of Davis.
either way Davis dies and Zod shows up next season