The get API is useful for retrieving a document when you already know the ID of the document. It is essentially a get by primary key operation, as follows:

GET /catalog/_doc/1ZFMpmoBa_wgE5i2FfWV

The format of this request is GET /<index>/<type>/<id>. The response would be as expected:

{
  "_index" : "catalog",
  "_type" : "_doc",
  "_id" : "1ZFMpmoBa_wgE5i2FfWV",
  "_version" : 1,
  "_seq_no" : 4,
  "_primary_term" : 1,
  "found" : true,
  "_source" : {
    "sku" : "SP000003",
    "title" : "Mastering Elasticsearch",
    "description" : "Mastering Elasticsearch",
    "author": "Bharvi Dixit",
    "price": 54.99
  }
}