Hi,
Filtering on the Joomla user group is not easy because a joomla user can have several groups.
So you should add extra tables in the order listing query in order to link the Joomla table an the user groups.
To do so, you have to use a custom plugin and the HikaShop trigger "onBeforeOrderListing".
function onBeforeOrderListing($paramBase, &$extrafilters, &$pageInfo, &$filters, &$tables, &$searchMap) {}
It will allow you to add filters (in the interface and the query) and new elements for the search map.
Otherwise, thanks to a view override, you can use the order objects and perform a query to add a new column and display the corresponding Joomla user groups.
Regards,