The issue with your request is that the X-Knack-Application-Id and X-Knack-REST-API-KEY are headers and need to be sent as such instead of as part of the URL. If you are using jQuery ajax ($.get or $.ajax), you can provide these headers under the header key in your options.
Please do note, however, that you should not use your API key in any client-side code (the Javascript section of your Knack app). Instead, use view-based API calls, as described here.
Feel free to reach out at david@hmnd.io if you need any further assistance with this or anything else.