This Alexa skill says current GMT. Alexa skill can be broadly classified in two parts. One has declaration of intent schema, sample utterance and it points to the second part i.e. AWS Lambda. The AWS lambda does the heavy lifting of processing intent(s), performing logical operations and finally composing the sound and returning it as JSON.
The details can be found on my blog.
This file shows the schema for intents. It specifies two intents, ZuluTime (returns Zulu time) and help intent.
This maps human utterances to intents.
This gets invoked with user says the utterances. It does the processing of the intents.