Hi!
Encoding of request and response messages are specified in the <binding> element of a WSDL. In that element you will be able to see <body> elements belonging to the namespace
http://schemas.xmlsoap.org/wsdl/soap/ (for WSDL 1.1). The value of the use attribute specifies the encoding.
An example:
Note that the WS-I Basic Profile only allows for literal encoding!
If you want to enclose character data encoded using some other character encoding scheme in a web service request or response, then you may want to encode that data using, for instance, Base64 before sending it in a SOAP message and then decoding it, of course, once it arrives at its destination.
Best wishes!