var viewModel;

// result could look like this: "{ "personId": 1, "firstName": "Marco", "lastName": "Franssen", "age": 26, "webpage": "http://marcofranssen.nl", "twitter": "@marcofranssen" }"$.ajax({
    url: 'http://somewebpage.net/getPerson'
    type: 'GET',
    dataType: 'JSON',
    success: function (result) {
        var data = JSON.parse(result);
        viewModel = ko.mapping.fromJS(data);
        ko.applyBindings(viewModel, $('#person').get(0));
    },
    error: function (result) {
        //handle the error, left for brevity
    }
});