Hi, I would like to enquire if my SQ air ticket is not firm ( sub load) can I take the ferry from Macau direct to Hongkong airport.

If you do not have a valid airticket with confirmed the seat, you cannot use the ferry from Macau to HKIA directly, according to the rules.
You can take a ferry for HK Macau Ferry Terminal and the use HK local public buses to reach HKIA. The HK Macau Ferry Terminal is at the Sheung Wan area, so you can take the Island Line to Central Station and then walk to the HK Station to take the Airport express to HKIA.