Well, by the looks of it, almost the entirety of the talk.
Seriously though, are you kidding me? The author of the rebuttal criticises Slavoj principally for not offering alternatives and for not fleshing out his ideas fully. This animation is 10 minutes long. Do you seriously think that Slavoj went to give a talk at the RSA which lasted 10 minutes? Give the man a break. I highly doubt that in his talk, which featured questions from audience members and panelists, he did not address any of these questions at all.
If you want a more precise answer of what the author missed, then I doubt it would be possible to condense this to a 'smidgen'. This is not a small topic and I suggest that if either you or the author of the rebuttal want a decent idea of Zizek's ideas regarding society then reading his work would be a better start than watching a 10 minute animated clip.
The thing that has been doing the rounds of the internet is the 10-minute animated clip, not whatever longer talk Žižek may have given, nor the entirety of any of his books (still less his whole oeuvre).
It seems perfectly reasonable to write a rebuttal of that.
Of course it might fail to be a good rebuttal on account of considering only the 10-minute animation, in two ways. (1) By criticizing Žižek for failing to do something that in his fuller work he actually has done. (2) By rebutting with bad arguments that Kaufman would have discovered to be bad, had h...
Since repositories are popular and useful, I thought it would be good to have one where we pair common bad/incorrect/flawed/misleanding/incomplete ideas with high-quality articles that explain why those ideas are bad/incorrect/flawed/misleading/incomplete.
Examples:
Myers-Briggs as a theory of personality. -> Richard Batty's "The Myers-Briggs type Indicator: A Popular But Flawed Way of Understanding Your Personality" from 80000 Hours.
Microfinance -> Ben Todd's "Is Microfinance Mostly Hype?" and GiveWell's "6 Myths About Microfinance Charity Donors Can Do Without".
Zizek's talk on charity "First as Tragedy, then as Farce" (or the idea that charity is bad because it undermines political change) -> Jeff Kaufman's "Good Charity as Neither Tragedy or Farce".
The idea that the AI will be benevolent/Friendly by default. -> Luke and Louie's "Intelligence Explosion and Machine Ethics".
etc.