Apex REST response with reserved words

Use JSON2Apex with the 'Create explicit parse code' option enabled. This will produce code like so:

//
// Generated by JSON2Apex http://json2apex.herokuapp.com/
//

public class MyList {
    // ...boilerplate...

    public class List_Z {
        public String id {get;set;}

        public List_Z(JSONParser parser) {
            while (parser.nextToken() != JSONToken.END_OBJECT) {
                if (parser.getCurrentToken() == JSONToken.FIELD_NAME) {
                    String text = parser.getText();
                    if (parser.nextToken() != JSONToken.VALUE_NULL) {
                        if (text == 'id') {
                            id = parser.getText();
                        } else {
                            System.debug(LoggingLevel.WARN, 'List_Z consuming unrecognized property: '+text);
                            consumeObject(parser);
                        }
                    }
                }
            }
        }
    }

    public List<List_Z> list {get;set;}

    public MyList(JSONParser parser) {
        while (parser.nextToken() != JSONToken.END_OBJECT) {
            if (parser.getCurrentToken() == JSONToken.FIELD_NAME) {
                String text = parser.getText();
                if (parser.nextToken() != JSONToken.VALUE_NULL) {
                    if (text == 'list') {
                        list = new List<List_Z>();
                        while (parser.nextToken() != JSONToken.END_ARRAY) {
                            list.add(new List_Z(parser));
                        }
                    } else {
                        System.debug(LoggingLevel.WARN, 'Root consuming unrecognized property: '+text);
                        consumeObject(parser);
                    }
                }
            }
        }
    }

    //...etc...

Just replace all occurrences of the list member variable with list_z (or whatever you like), and you're off to the races:

//
// Generated by JSON2Apex http://json2apex.herokuapp.com/
// Hand-modified by @metadaddy :-)
//

public class MyList {
    // ...boilerplate...

    public class List_Z {
        public String id {get;set;}

        public List_Z(JSONParser parser) {
            while (parser.nextToken() != JSONToken.END_OBJECT) {
                if (parser.getCurrentToken() == JSONToken.FIELD_NAME) {
                    String text = parser.getText();
                    if (parser.nextToken() != JSONToken.VALUE_NULL) {
                        if (text == 'id') {
                            id = parser.getText();
                        } else {
                            System.debug(LoggingLevel.WARN, 'List_Z consuming unrecognized property: '+text);
                            consumeObject(parser);
                        }
                    }
                }
            }
        }
    }

    public List<List_Z> list_z {get;set;}

    public MyList(JSONParser parser) {
        while (parser.nextToken() != JSONToken.END_OBJECT) {
            if (parser.getCurrentToken() == JSONToken.FIELD_NAME) {
                String text = parser.getText();
                if (parser.nextToken() != JSONToken.VALUE_NULL) {
                    if (text == 'list') {
                        list_z = new List<List_Z>();
                        while (parser.nextToken() != JSONToken.END_ARRAY) {
                            list_z.add(new List_Z(parser));
                        }
                    } else {
                        System.debug(LoggingLevel.WARN, 'Root consuming unrecognized property: '+text);
                        consumeObject(parser);
                    }
                }
            }
        }
    }

    //...etc...

Note - you'll also need to move the test code into its own class. Superfell or I need to go back and fix that. We should also rename the member variable when it clashes with a reserved word.

Anyway - now you can create a MyList from JSON like so:

MyList l = MyList.parse(json);

Salesforce Apex and other languages like Java, C etc will give you errors when you try to use reserved words.

However as you said that this response is really required so here is what I suggest.

1. Rename the list to something unique example: list_replace_me

   global List<DataWrapperClass> list_replace_me;
   

2. Instead of returning the wrapper from your GET method, return a string.

   global static string getList() { 
   //Manually serialize this object
   
   new ResponseWrapperClass(); } 
   

3. Manually serialize the object by JsonGenerator class to get a string, or use JSON.serialize(inputobject) which return a string.

4. Replace "list_replace_me" with "list" using String.replace function.

5. Return the new String after replacing.

Json Generator