I don't think the North Korean government would have standing in a US court.

Though US government claims standing in UK court to take Assange.

We signed an extradition treaty in 2003 with the UK:

The Parties agree to extradite to each other, pursuant to the provisions of this Treaty, persons sought by the authorities in the Requesting State for trial or punishment for extraditable offenses.

https://irp.fas.org/world/uk/extradite.pdf

As I understand it, this was an extension of the original 1972 treaty.

NK committed a sovereign act of war, not a crime. NK is not under common jurisdiction as the victim.