eikh hu oseh et zeh
Is there any difference in usage between כיצד and איך?
Only that כיצד is more formal.
how do you pronounce כיצד?
The voice actor really delivers this one with appropriate astonishment!
How about ככה הוא עושה את
Not really. ככה means "like this", so you kinda wrote "like this he does ..." and left it unfinished, since את has to be followed by an object.
why is it et zeh, not just plain zeh?
It's just how זה works as a direct object. It requires את.