user_access() replaced with a method on the user/accountInterface

The user_access() method was directly replaced by AccountInterface::hasPermission(). Most of the time, this account is the current user session, which can be accessed via the account attribute on the current request.

If you have a user entity, you can also use the same method.

Drupal 7

user_access('name of permission');

$account = user_load('3');
user_access('name of permission', $account);

Drupal 8

\Drupal::currentUser()->hasPermission('name of permission');

$account = user_load('3');
$account->hasPermission('name of permission');