Hi Anirudh, welcome to the Community!
Confluence Server still has a REST API for the Questions for Confluence add-on. It's available here - while the document seems like it might be out of date based on the old Confluence logo, it's just because the end-points have been stable since Questions 2.3. The API is still available in the most recent release for Server, Questions for Confluence 2.7.
Daniel | Atlassian Support
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