Who pays the stamp duty in Hong Kong? And how much is paid?

The purchaser and seller are both responsible for paying the stamp duty. However, the purchaser will usually contract to pay the stamp duty in full.

The table below shows the stamp duty tax rate for commercial properties, after 20 November 2020. More details on the amount payable can be found here

Amount or value of the consideration(whichever is the higher)Stamp duty tax rate for non-residential properties. 
ExceedsDoes not exceed
 $2,000,000$100
$2,000,000$2,351,760$100 + 10% of excess over $2,000,000
$2,351,760$3,000,0001.5%
$3,000,000$3,290,320$45,000 + 10% of excess over $3,000,000
$3,290,320$4,000,0002.25%
$4,000,000$4,428,570$90,000 + 10% of excess over $4,000,000 
$4,428,570$6,000,0003%
$6,000,000$6,720,000$180,000+ 10% of excess over $6,000,000 
$6,720,0003.75%

You should note that the calculation of stamp duty for residential property is different.