To locate a particular Gemini entry for a node, you need to know the uuid of the node. You can get the uuid for the node by looking at the devel tab in Drupal or you can get it from json representation: http://localhost:8000/node/2?_format=json.
You can look up Gemini entries for node using the Gemini service via curl or a REST client such as POSTman.
curl -H "Authorization:Bearer islandora" http://localhost:8000/gemini/uuid_value
Alternatively, you can login to mysql database, select the gemini database and issue the following query:
select * from Gemini where uuid="uuid_value";