Listing a set is handled by the listSkylarkSet query.

This example shows getting a list of sets with their title, uid and contents.

query listSkylarkSet {
  listSkylarkSet {
    objects {
      uid
      title
      content {
        objects {
          __typename
          uid
          ... on Episode {
            external_id
            slug
            title
            synopsis
          }
          ... on Season {
            external_id
            title
          }
        }
      }
    }
  }
}