As suggested at the OGC API - Common session of the 127th Members Meeting in Singapore:

It would be great if Part 2 could include a conformance class for "schemas" that would describe the properties / field of the collection of geospatial data, in line with what Features is defining in Part 5: Schemas ( opengeospatial/ogcapi-features#740 ).

This could be kept to a minimum:

• guidance for link relation types to link to the schema
• specifying that a JSON representation of the schema will be a JSON Schema
• specifying the /collections/{collectionId}/schema resource ?
• specifying the x-ogc-* mechanism for extending JSON Schema with semantic annotations

We are now also using this approach in OGC API - Coverages to describe the fields of the coverage.