Unless someone on the forum already has the API you will have to contact Hikvision support directly to see if they will share it with you. Hikvision are quite controlling/protective of their API and will probably require you to register as an integration/software developer before they share it with you.
If the content you need is not included in any of SDK files available from Hikvision then you will need to contact them directly to get developer access to the the API/SDK files for the intercom range.