In the book when Tom visits Johnny Tom tell him that he should start his own production company and create movies. Tom tells Johnny that the Don will finance him but well ask him for a favor in return. In the book Tom wonders whether Johnny will be smart enough to figure out that the favor wont be from the Don or something. (I cant find my book so sorry if i make no sense) WEll what was the favor?

The gist of that passage was that, after the Don had Khartoum's head cut off, Woltz was forced to put Johnny back in that war movie. But Woltz wasn't going to spend any money to help Johnny win an Academy Award for his performance. Hagen was in Hollywood with Johnny to assure him that the Don would support his winning the Award by using influence. Then Johnny said he wanted to be a producer. Hagen told Johnny to plan to produce 3-5 pictures, and when he needed money, to call Hagen, who would give him the name of a bank (influenced by the Don) that would finance the pictures. "Is there anything else?" asked Johnny. "Do you mean, do you have to do anything in return?" replies Hagen. "Of course you do, but it wouldn't be anything that you wouldn't do for your Godfather if he asked you anyway." So, Hagen was telling Johnny three things: That his godfather had faith in him; that his godfather had vastly more power in Hollywood than Johnny imagined; and that there'd be a quid pro quo for the help. That came later, when Michael asked Johnny to sign a contract to appear at the Corleone-backed hotel several times a year to bring in gamblers.

the "secret favor that´s not mentioned" is, i think, meant to be fontane takinG his childhood pal nino valenti to tinseltown and make him biG. at connie´s reception he complains to his Godson how he forGot his old friends, especially nino. in the book, when fontane decides to call nino and offers to make him biG in the movies, he recalls the conversation with tom and smiles about how smart his Godfather is.

i really love the tom/fontane scenes thouGh they´re completely uninterestinG storywise. i like the fact that they are both "extra sons" to the Don and so different in character they piss each other severely off.

For me, the most interesting line in the Tom-Johnny exchange is, "I guarantee you that any favor he asks of you, you will offer to do it before he requests it. Okay?" It's obvious that Tom is talking about himself, and how he felt when he went to the Don and offered to work for him. After Vito had saved him, Tom could do nothing else.