We know of the Kelly - Trump ego dustup, but with Trump so targeted, the FOX folks were so focused they omitted:
Rick Santorum:
Why were you voted out of office in Pennsylvania?
Scott Walker:
Where did the money come from so you could barely survive the impeachment effort?
Ben Carson:
What were your malpractice insurance rates when you were practicing medicine?
Carley Fiorina:
Why did the HP board fire you, and why did you do so poorly running against Senator Boxer?
Ted Cruz:
Aren't you a Canadian?
Jeb!
Do you still contend your interference in the Schiavo family's most difficult affairs was a proper exercise of government power and can we anticipate you'd do that same kind of thing again?
Lindsey Grahm:
Is your 1% approval ratings in the polls because you've been a DC insider, career politician your entire life?
Rand Paul:
Do you see people regarding you as being as consistent and trustworthy as your father, and what about his buying that guy in Iowa away from Bachmann?
Gov. Kasich:
Would you even have squeaked in here in the top ten if this event were not in Ohio?
Marco Rubio:
Is having two candidates from the same state counter productive, and do you suggest the other should step aside?
Perhaps one or two of those is a bit weak; but the only gotcha target was the frontrunner; and it seems strange FOX would put itself into looking unfair; ill-balanced; that way.
____________UPDATE_____________
Having never suggested I'd watched the show, I may be wrong, and arguably a range of unhelpful gotcha questions may have been catered, sauced to flavor, where I have to believe Breitbart [yes, of all sources] is being factually correct. Perhaps more balanced than I'd thought from other reporting, perhaps less fair in phrasing neutral questions without lead-in editorializing where the show was about the candidates with the term "hosting moderators" being linguistically akin to "moderate," and their participation not being called "hosting provocateurs."