How is the tourist visa procedure for Sri Lankan passport holders?

Upek, the proofs from the sponsor are not necessarily required for submission, but if you can provide them, it will be better.

You can submit the application documents to the embassy in Sri Lanka or ask your friend to submit the documents for you to the HK Immgration Department. The application documents include passport, passport copy, recent photo, application form, financial standing proof copy, photocopy of round-trip tickets, itinerary, etc.