cat input_file.json | jq 'length'

{
  "entity_id_01": {
    "field_a": "value_a",
    "field_b": "value_b",
    "field_c": "This is a generic feedback message"
  },
  "entity_id_02": {
    "field_a": "value_a",
    "field_b": "value_b",
    "field_c": "This is a generic feedback message"
  }
}