How to pass text from alexa/echo to a server
It is not easy, unfortunately and by design.
User responses are stored in word 'slots' in the interaction model. This is how Alexa parses speech and execute commands based on user utterances. Without knowing every variation of a possible word slot and writing this into your interaction model, you won't be able to store free form text in a variable and 'pass it on'.
It's not possible. The closest you can get there is by using the built-in slot type AMAZON.Literal (US only and deprecated) or AMAZON.SearchQuery (available in all locales). I say "closest" because SearchQuery for example requires a carrier phrase in the utterance besides the slot (it can't be there alone capturing everything).
Note that the free form capture provided by these types is less accurate than if you define a custom slot type (i.e. you know more or less what you want to capture)