Drupal 7.61 and PHP 7.2 effect on modules

Current Website:

PHP 7.2.10    (php -v)
ubuntu 18.04.1 LTS bionic    (lsb_release -a)
Apache 2.4.29    (apache2 -v)
Drupal 7.61     (drush status)
Drush 6.2.0     (drush status)
Mysql Ver 14.14 Distrib 5.7.24   (mysql -V)

When I run (on the command line): drush status I get 21 identical lines of:

count(): Parameters must be an array or an object that implements Countable Table.php: 699

Assuming that Drupal 7.61 is complete for PHP 7.2 then these messages must come from modules (not CORE)?

How do I detect which modules are not ready for PHP 7.2?

I am not a programmer: I am not seeing PHP errors displayed. Do I need to turn-on PHP errors?

Is there a PHP error log?

When I run (on the command line): drush ws I get 6 identical lines of:

mollom       error      API keys could not be verfied.     Error 900    Network error (rest.mollom.com) etc

Other than the above my website appears to be running ok.

Comments much appreciated.


Drupal version: 

Source: https://www.drupal.org/taxonomy/term/21/feed