I know for a fact that saved Kibana dashboards (ie, the JSON file of the dashboard) are saved in OR associated to a particular ElasticSearch
For kibana 4, I found the default index value in config/kibana.yml file and it was ".kibana"
Following is the line from kibana configuration file.
kibana_index: ".kibana"
And here is the query that displayed me the required results
curl -XGET http://localhost:9200/.kibana/_search?type=dashboard&pretty=1