Address what Dworkin says, or would say, in reply to the defenders of Hart who say that Hart’s theory can absorb his criticisms.

It is certainly relevant to describe Hart’s theory.
On the subject of structure, you need to:
i) Describe Hart’s theory
ii) Describe Dworkin’s theory
iii) Address the question of the extent to which Dworkin’s theory really undermines Hart’s (this is relevant to the part of the question that asks whether Dworkin’s theory provides ‘a genuine alternative to positivism’). Many defenders of Hart claim that Hart’s theory can, so to speak, absorb Dworkin’s criticisms without being undermined. (What this really comes down to is that defenders of Hart say that principles can be incorporated in a system of primary and secondary rules with a rule of recognition. Dworkin, however, claims that principles can’t be so incorporated.)

iv) Address what Dworkin says, or would say, in reply to the defenders of Hart who say that Hart’s theory can absorb his criticisms. This is where the arguments of the Model of Rules II become relevant.

In performing these tasks you may find especially helpful – in addition to Hart’s and Dworkin’s own writings – the essay by Shapiro called ‘The Hart-Dworkin Debate: a Short Guide for the Perplexed’. This gives a useful overview of the debate.The most impressive thing you could do, in a way, would be to disagree with some aspect of Shapiro’s account of the debate.