Filter on child types

Try requesting some variables on pet

query TheQuery {
  getHuman @cascade{
    id
    name
    pet(filter: {typeOf: {eq: "dog"}}) {
      id
      typeOf
      name
    }
  }
}

But generally speaking, what you wrote should work. You also may not need @cascade, depending on your data.

https://dgraph.io/docs/graphql/queries/search-filtering/

J