In Man of Steel Kal-El triggers the homing beacon on the scout ship, this signal is picked up by Zod who then travels to Earth. Zod explains this is how he is here but not how he knew Kal-El was also here.
When he reaches Earth he insists that humanity hands over Kal-El as he is a wanted criminal, he also states that he knows Kal-El has not revealed himself to the world and has lived among them as one of them.
How does he know all this information?
- He didn't know where Jor-El had sent his son, if he had he would have gone straight there.
- He can't detect the pod Kal-El landed in, if he could he would have gone straight there and wouldn't have had to take it from Lois Lane's mind.
There is no evidence that Kal-El has been on Earth for Zod to detect, it is just as, if not more likely that humanity found the scout ship and triggered something in it. If Kal has been living in secret there is an equal chance he just isn't there at all.