Correct way to define array of enums in JSON schema

Option A is correct and satisfy your requirements.

{
    "type": "array",
    "items": {
        "type": "string",
        "enum": ["one", "two", "three"]
    }
}

According to json-schema documentation, the enumerated values of an array must be included in the "items" field:

{
    "type": "array",
    "items": {
        "type": "string",
        "enum": ["one", "two", "three"]
    }
}

If you have an array that can hold e.g. items of different type, then your schema should look like the one below:

{
  "type": "array",
  "items": [
    {
      "type": "string",
      "enum": ["one", "two", "three"]
    },
    {
      "type": "integer",
      "enum": [1, 2, 3]
    }
  ]
}