Get Twig Version
If you want to check the used version of Twig, you can enter this line to one of your template files:
<p>Twig version is {{ constant('Twig_Environment::VERSION') }}</p>
Another option is to check the file vendor/twig/twig/lib/Twig/Environment.php or vendor/twig/twig/src/Environment.php, depending of the version you use. In one of the two files, a there is a version constant:
const VERSION = '2.12.2';