Programmatically get all GraphQL schemes

If I understood you correctly, you are asking about Introspection Queries.

For example, the following GraphQL syntax-text is asking the GraphQL server to return a list of all queries available to us from the schema:

{
  __schema {
    queryType {
      fields {
        name
      }
    }
  }
}

Returns all mutations available to us from the schema:

{
  __schema {
    mutationType {
      fields {
        name
      }
    }
  }
}

Returns the entire schema: queries, mutations, fields, etc.:

GraphQL Endpoint Introspection Query gist

query IntrospectionQuery {
    __schema {
      queryType { name }
      mutationType { name }
      subscriptionType { name }
      types {
        ...FullType
      }
      directives {
        name
        description
        args {
          ...InputValue
        }
        locations
      }
    }
  }
  fragment FullType on __Type {
    kind
    name
    description
    fields(includeDeprecated: true) {
      name
      description
      args {
        ...InputValue
      }
      type {
        ...TypeRef
      }
      isDeprecated
      deprecationReason
    }
    inputFields {
      ...InputValue
    }
    interfaces {
      ...TypeRef
    }
    enumValues(includeDeprecated: true) {
      name
      description
      isDeprecated
      deprecationReason
    }
    possibleTypes {
      ...TypeRef
    }
  }
  fragment InputValue on __InputValue {
    name
    description
    type { ...TypeRef }
    defaultValue
  }
  fragment TypeRef on __Type {
    kind
    name
    ofType {
      kind
      name
      ofType {
        kind
        name
        ofType {
          kind
          name
        }
      }
    }
  }