In GraphQL an enum represents a list of available values for specific type.

enum Sort {
+  NAME_ASC # GOOD
-  nameAsc # BAD
-  NameAsc # BAD
   NAME_DESC
   AGE_ASC
   AGE_DESC
}

For example, GraphQL uses __TypeKind enum with values SCALAR, OBJECT, INPUT_OBJECT, NON_NULL in Introspection queries. So CAPITALIZED_WITH_UNDERSCORES is being used for enum types.

If we think about the enum type as a set of constants, almost all programming languages use CAPITALIZED_WITH_UNDERSCORES to define constant values.

Naming enums in CAPITALIZED_WITH_UNDERSCORES style makes it easy to spot them in GraphQL queries:

query {
  findUser(sort: ID_DESC) {
    id
    name
  }
}

This rule can be validated using graphql-eslint, read more about naming-convention rule.