Ceo of sport is still not Juventus CEO. Its the head of a division. The question I have is who is actually in charge? Coul Marotta have fired Agnelli? or Paratici? Could Agnelli fire Marotta or are they all under someone?
We had joint CEOs like Inter does now. Aldo Mazzia was the "CEO of Finance - CFO." That was literally his title in the Board of Directors page. Marotta's was CEO of Sport.
Post-Marotta and -Mazzia, we're yet to appoint a new CEO.
The CEO(s) works under the President or owner of course (I'm surprised you didn't know that, these are some weird q's).
As for Khedira, Marotta had full autonomy when it came to the squad. Agnelli only set the budget (total budget per season for salaries & transfer fees - same, not separate). Agnelli himself had said so. Ronaldo was an anomaly. But now, according to rumors/reports, Agnelli will have to sign off on the big purchases (like Ronaldo), Nedved's signature will be needed for some range below that, and Paratici has full autonomy on amounts below that.
Hope that clears everything up.