Hi there,
Product listing don't display custom field by default.
If you want to do so, you'll have to add some code to one of this view (Display>View). For example in product/listing_div, you can load the customs fields with:
$itemFields = $this->fieldsClass->getFields('frontcomp',$this->row,'product','checkout&task=state');
and then display it with:
foreach($itemFields as $fieldName => $oneExtraField) {
if(!isset($this->row->$fieldName)) continue;
echo $this->fieldsClass->show($oneExtraField,trim($this->row->$fieldName));
}