main.tf

data "terraform_remote_state" "root" {
    backend = "local"
    config = {
        path = "../terraform.tfstate"
    }
}


output "message" {
    value = "hello ${data.terraform_remote_state.root.outputs.config.person.name}!!"
}

terraform.tfstate

{
  "version": 4,
  "terraform_version": "1.0.2",
  "serial": 2,
  "lineage": "79b020dd-1206-1cf8-3423-607b18805204",
  "outputs": {
    "message": {
      "value": "hello foo!!",
      "type": "string"
    }
  },
  "resources": [
    {
      "mode": "data",
      "type": "terraform_remote_state",
      "name": "root",
      "provider": "provider[\"terraform.io/builtin/terraform\"]",
      "instances": [
        {
          "schema_version": 0,
          "attributes": {
            "backend": "local",
            "config": {
              "value": {
                "path": "../terraform.tfstate"
              },
              "type": [
                "object",
                {
                  "path": "string"
                }
              ]
            },
            "defaults": null,
            "outputs": {
              "value": {
                "config": {
                  "person": {
                    "age": 20,
                    "name": "foo"
                  }
                }
              },
              "type": [
                "object",
                {
                  "config": [
                    "object",
                    {
                      "person": [
                        "object",
                        {
                          "age": "number",
                          "name": "string"
                        }
                      ]
                    }
                  ]
                }
              ]
            },
            "workspace": null
          },
          "sensitive_attributes": []
        }
      ]
    }
  ]
}