Does a Sri Lankan transitting in Hong Kong need a visa?

Yes, Natalie, you need to apply for an transit permit for Hong Kong in advance. You can go to the embassy and submit the following materials:
1. Application form (ID 1003A)
2. Your recent photograph (affixed on page 1 of the application form ID 1003A)
3. Photocopy of your passport
4. Photocopy of proof of your financial standing, e.g. bank statements, savings accounts passbooks, tax receipts, etc. and proof of employment (if any), e.g. company leave letter, salary slips, etc.
5. Photocopy of flight itinerary
6. Photocopy of proof of the proposed visit in the next destination after visiting Hong Kong, itinerary, etc.