The requirements for China business visa application in Hong Kong are:
Your valid actual passport. The passport must have at least six (6) months validity left before expiration and at least one blank page left in it.

One completed Visa Application Form with one additional passport photo (black & white or color is acceptable).

Visa Notification Form, or an letter issued by the company he/she is employed and the registration license of this company, or an invitation letter from the mainland company ant the registration license of this company.

Under some circumstances, the applicants may be required to provide financial proof, a copy of Chinese hotel booking and return flight ticket booking.
You can go to the Commissioner's Office of Foreign Affairs Ministry of PRC in Hong Kong SAR Government to apply for China business visa
Address
7th Floor, Lower Block, China Resources Building,
No.26, Harbor Road, Wanchai, Hong Kong SAR