How can get path of image (src) in twig template of a module?
You need to use file_create_url much like Drupal 7 to transform a file path to file url. To get the path to the module, you should use drupal_get_path, combined it could look like this:

function my_module_preprocess(&amp;$variables, $hook) {
  $variables['img_path'] = file_create_url(drupal_get_path('module', 'my_module') . '/image/icons/my-image.svg');
}