Depending on which version of ICN and CMOD/ODWEK you have installed, the default viewer map should work fine, provided you want the HTML Line Viewer as your view type (this assumes that your desktop has the Default viewer map selected). Incidentally, download as 'As UTF8' should also give you readable output. Download 'As original' is probably EBCDIC since this is JCL output.
You can check this by going to the ICN Admin desktop, select Viewer Maps and then double click the Default viewer map, Then scroll down to the 1st occurrence where the Repository Type is Content Manager OnDemand and the File type is application/line and verify that it shows Line Data HTML Viewer in the Viewer column. If this is correct, you likely already have a properly configured viewer map.
Make sure you are using a supported browser (pretty much everything but Internet Explorer).
If that all looks ok, check the browser console for any errors. You can launch the browser console by entering control+shift+i at the search results screen and then right-click on the doc and select Open. If you see errors in the browser console, you should reopen your case with IBM and them know what those errors are.
For what it's worth, there have been many changes to the HTML Line Viewer so if you are back level in either CMOD/ODWEK or ICN, I would highly recommend upgrading.