From my testing, it does it by default. So I followed this page: https://developers.coveo.com/display/public/SitecoreV4/Provide+Result+Suggestions and I added the "Coveo Search Resources", "Coveo Search Box" and "Coveo Omnibox Result List" to my header. I now have suggestions on everything within my index.

Side Note : The suggestions, when clicked, will open the result itself, it will not redirect me to the search page.

I tested just typing "ar" and it suggested **Ar**ticle , **Ar**ticle Group, Gloss**ar**y and more.

Is it what you are seeing?

*** UPDATE ***

I made a mistake in my original answer, I was using field-based **query** suggestions : https://developers.coveo.com/display/SitecoreV4/Provide+Query+Suggestions#ProvideQuerySuggestions-FieldBasedSuggestions

To have the same query completion behavior with the OmniboxResultList (Results Suggestions) is not possible without adding a wildcard, since it does a full query against the index, while query suggestions does a field listing call:
https://developers.coveo.com/display/SearchREST/Listing+Values+of+a+Field

So is there a workaround? Yes!

The way it work on our pages such as the [online help][1] is by doing a field-based query with a custom onSelect event, which looks like this:

<!-- language: lang-js -->

    // Initializing the search box
    $('#searchBox').coveo('initSearchbox', MySearchBoxComponent, {
        FieldSuggestions: {
            // Initialize the Omnibox
            omniboxSuggestionOptions: {
                onSelect: function (valueSelected, populateOmniBoxEventArgs) {
                    populateOmniBoxEventArgs.closeOmnibox();
                    // When a value is selected, query the index for the result list
                    Coveo.SearchEndpoint.endpoints["default"]
                        .search({
                        q: '@systitle=="' + valueSelected + '"',
                        aq: SuggestionScope
                        })
                        .done(function (results) {
                            var foundResult = Coveo._.find(results.results, function(result){
                                    return valueSelected == result.raw.systitle;
                                });
                            // If you find a result, log the Analytics event and navigate to the result clickable uri
                            if(foundResult) {
                                logCustomEvent('pageNav', 'omniboxTitleSuggestion', uaToken, foundResult.Title, foundResult.clickUri);                                  
                                window.location = foundResult.clickUri;
                            } else {
                                logger.warn("Selected suggested result," + valueSelected + " , not found.");
                            }
                        })
                },
                // Add a query override to the Omnibox on the current suggestions
                queryOverride: SuggestionScope
            }
        }
    });

So what it does is offering query suggestions, but instead of redirecting to the result page, it queries the index and redirects to the most relevant result.

For more information on the PopulateOmnibox function: https://developers.coveo.com/display/JsSearchV1/Providing+Suggestions+for+the+Omnibox



  [1]: https://onlinehelp.coveo.com/en/home.htm