BuddyPress activity on edit post for a CPT

Use the save_post hook. Try something like:

function jude_classified_activity_entry( $post_id, $post, $update ) {

    $slug = 'classified';

    if ( $slug != $post->post_type )
        return;

    bp_activity_add( 
      // etc
    );

}
add_action( 'save_post', 'jude_classified_activity_entry', 15, 3 );