Box 18 should show the codes for the country or countries, other than the UK, in which your wife is resident for tax purposes for 2021 to 2022.
Box 19 should be left blank if your wife was not resident in Hong Kong in 2020 to 21.
Boxes 20 to 22 are for tax relief being claimed. If no relief is being claimed, then leaave them blank. You can see guidance notes here:
Residence, remittance basis etc notes