var_dump on $item will provide:
protected '_data' =>
array (size=18)
'id' => int 1
'class' => string 'IPS\forums\Topic' (length=16)
'class_id' => int 96
'text' => string '{"internal":"In regard to money matters C\u00e6sar was entirely without principle. In his early years he borrowed vast sums on all sides, spent them recklessly, and seldom paid his debts save with further borrowed money. While still a young man he owed his creditors the sum of \u00a3280,000; and though most of this had now been paid off by means of the loot from the Gallic Wars, there had been times in his life when ruin stared him in the face. Most of his debts were incurred in the first place in buying fo'... (length=1089)
'short_link' => string 'http://localhost/45X/index.php?/topic/96-motivational-genus-porzana/' (length=68)
'media' => string '[]' (length=2)
'added' => int 1619437470
'scheduled' => int 1619437470
'sent' => int 1619437472
'added_by' => int 1
'schedule_auto' => int 0
'share_to' => string '["internal"]' (length=12)
'images' => string '[]' (length=2)
'returned' => string '{"internal":1619437472}' (length=23)
'failed' => int 0
'internal' => int 1
'form_data' => string '{"internal":{"title":""}}' (length=25)
'hide' => int 0
So $item->class will give you the class. For this example, IPS\forums\Topic.
Btw, I used this in promotePublicTableRow Core template. Not sure if $item in yours is the same.