I had this exact question. And for methods like get I figured it out.
Create your client and then do the following
api = client.discovered_api("admin", "directory_v1")
puts "--- Users List ---"
puts api.users.list.parameters
puts "--- Users Get ---"
puts api.users.get.parameters
This will print off the parameters. You can also use api.users.get.parameter_descriptions
Something that could be helpful if you are trying to probe into issues like this is to print off all the available methods. I typically do it like this.
puts api.users.insert.methods - Object.methods
If you try that one you will see that api.users.insert has the following methods after you take away the ones that are common to every object.
discovery_document
api
method_base
method_base=
description
id
http_method
uri_template
media_upload
request_schema
response_schema
normalize_parameters
generate_uri
generate_request
parameter_descriptions
parameters
required_parameters
optional_parameters
validate_parameters
I hope that helps.
James