Get Commentor IP When Marking Comment As Spam

You are missing 2 parameters in your function report_spam. Also the priority should not be 1. Try the code below.

add_action('transition_comment_status', 'report_spam', 10, 3);
function report_spam($new_status,  $old_status, $comment){
    if($new_status == 'spam'){
        var_dump($comment->comment_author_IP);
        die;
    } 
}

I’ve set die so that you can check and manipulate what you want.