I don't have sponsor in hong kong, what i should write for the reason when i apply for tourist visa?

The sponsor in Hong Kong is not mandatory for Hk visit visa application. If the visa officer asks you to provide the invitation and sponsorship letter from a sponsor in Hong Kong, it means that the officer suspects you will overstay in Hong Kong. The visa rule for nationals of different countries is different. I think the rule for Iraqi passport holders is very strict.