Hi,
the best way is to edit profile template and add manually SQL code to output.

You can use Joomla Template Override feature to do this:
- Copy /components/com_jsn/views/profile/tmpl/default_fields.php into /templates/your-template-folder/html/com_jsn/profile/default_fields.php
- Add a field of type HTML delimiter (example with alias "get_sql"
- in new file /templates/your-template-folder/html/com_jsn/profile/default_fields.php between lines 49 and 50 add something like this:

// LINE 49

if($field->fieldname=='get_sql'){

    $db=JFactory::getDbo();

    $query="SELECT value FROM #__your_table WHERE user_id=".(int) $this->data->id;

    $db->setQuery($query);

    echo $db->loadResult();

}

else

// LINE 50

With this the output of HTML delimiter will be replaced with your SQL value.

NOTE: This code is not supported and not tested.