Field Skip Map

There is no sample, but you can check the classic below for a general feel.

{
  "MigrationTools": {
    "Version": "16.0",
    "CommonTools": {
      "FieldMappingTool": {
        "FieldMaps": [
          {
            "FieldMapType": "FieldSkipMap",
            "ApplyTo": [
              "*"
            ]
          }
        ]
      }
    }
  }
}

{
  "$type": "FieldSkipMapOptions",
  "targetField": null,
  "ApplyTo": [
    "*"
  ]
}