No response from Services Entity API when added '.json' to the end of alias
Okey,

You shouldn't add the suffixes like .json or .xml to the end of the alias name like you do with some other resources if the resources are provided by services_entity module. Adding the suffix directly to end of the whole url solved it.

example.com/endpoint/resource_alias/resource_id.json ie:
example.com/api/entity_node/5.json