Do the Hong Kong protesters have asked for a modification to the proposed extradition law? Do they have any proposals for which circumstances might still justify extradition to China? What are they asking for? Do they want the extradition law to be cancelled or do they propose modifications?
The general way that extradition works is that the party requesting extradition (which I'll call China) goes to the entity that would do the extraditing (which I'll call Hong Kong) and demonstrates that a crime was committed. Note that this generally requires that the act be criminal in Hong Kong, not just China. Hong Kong could then evaluate that evidence in its court system. If Hong Kong found the evidence compelling, it would then extradite the alleged criminal to China.
The problem with the current version of "extradition" is that instead of being evaluated in a Hong Kong court, a representative of the Chinese government is simply allowed to approve extradition for crimes including things like protesting the Chinese government. Hong Kong had been promised "one country; two systems" but was getting the Chinese system.
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Protesters in Hong-Kong are not demanding for the proposed extradiction law to be modified. They are asking for the bill to be withdrawn altogether.
After the protests has gained momentum and authorities may have handled them ineffectively, other demands have come to the fore. Most notably, demonstrators ask for the Chief Executive of the government of Hong-Kong, Carrie Lam, to resign.