Do you mean to apply for a HKSAR Passport? You are eligible to apply for a HKSAR Passport if you are a Chinese citizen, have the Right of Abode (ROA) in the HKSAR and are holding a valid Hong Kong permanent identity card (PIC). And you must show the Hong Kong Birth Certificate if he was born in Hong Kong.
If you are residing overseas, application forms *(ID843) and Notes for Guidance can also be obtained from the Chinese Diplomatic and Consular Missions or the HKSAR Immigration Department. if you are over 16, a 10 year passport costs about HK$370; if you are under 16, a 5 year passport costs about HK$185.