within your main_part function in the qa-theme class look if you find something like this
elseif (strpos($key, 'q_list') === 0){
if so then change it with the following one
elseif (strpos($key, 'q_list') === 0){
foreach($part['qs'] as $key => $value){ //jdev this should set cat url on each question
$part['qs'][$key]['catpath']= implode('/', array_reverse(explode('/', $part['qs'][$key]['raw']['categorybackpath'])));
}
now within each question you have a key named catpath that you can display
i don't know which theme you use so i hope this help you.
this should work on the defaults themes