Schema.org is a collaborative, community activity with a mission to create, maintain, and promote schemas for structured data on the Internet, on web pages, in email messages, and beyond.
Schema.org markup is meant to enhance content blocks for search engines to categorize and display in the search engine results pages (SERP) as rich media. Schema.org markup is technically HTML wrapping of predefined tagging with contextual associations.
While it is technically possible to have hidden FAQs in structured data, doing so is against Google’s guidelines and can carry significant risks. A better approach is ensuring FAQ content is visible to users and optimized with structured data for Google. This creates a win-win scenario for search engines and your audience.