To clarify the previously posted note:

Dots (.) and spaces ( ) in cookie names are being replaced with underscores (_).

beware, dots (.) in cookie names are replaces by underscores (_)

The values of $_COOKIE in general are not identic with the values in $_SERVER["HTTP_COOKIE"]!

In phpinfo() $_SERVER["HTTP_COOKIE"] shows the actual value stored in the cookie by the browser in 7bit.
In $_COOKIE is this value after a 7bit to 8bit conversion.

When all characters in $_SERVER["HTTP_COOKIE"] are in ASCII = 7bit, $_COOKIE is displayed in phpinfo(). When one single character is not in ASCII, phpinfo() shows no value!

Although in $_COOKIE is still the 8bit conversion of $_SERVER["HTTP_COOKIE"]!
The reason: the 8bit conversion alone is not enough to say what characters are meant.
For that the used character-set is necessary.

phpinfo() does not know the character-set and better says nothing.

When using $_COOKIE in a php-generated web page the environment has the info of used character-set and so the meant characters can be displayed.

Three illustrating examples
===========================
A HTML-form is used to get the content which shall be stored in a cookie named "test".

Input string in field "test": door
$_SERVER["HTTP_COOKIE"]: test=door
$_COOKIE["test"]
   displayed in phpinfo(): door
   displayed in any html page: door

Input string in field "test" (ISO-8859-1 used in form): Tür
$_SERVER["HTTP_COOKIE"]: test=T%FCr
$_COOKIE["test"]
   displayed in phpinfo(): ""
   displayed in a ISO-8859-1-html-page: Tür
   (displayed in a UTF-8-html-page: T�r)

Input string in field "test" (UTF-8 used in form): Tür
$_SERVER["HTTP_COOKIE"]: test=T%C3%BCr
$_COOKIE["test"]
   displayed in phpinfo(): ""
   displayed in a UTF-8-html-page: Tür
   (displayed in a ISO-8859-1-html-page: Tür)

PHP replaces dots (.) with underscores (_). To find all original cookie names (and value) you can use $_SERVER['HTTP_COOKIE'].

For example to retrieve a cookie set with <?php setcookie('testing.dots', 'value'); ?> you may use:
<?php
    $cookies = explode('; ', $_SERVER['HTTP_COOKIE']);
    $allCookies = [];

    foreach($cookies as $cookie) {
        $keyAndValue = explode('=', $cookie);
        $allCookies[$keyAndValue[0]] = $keyAndValue[1];
    }

    var_dump($allCookies);
    /*
        array(1) {
            ["testing.dots"]=>
                string(5) "value"
        }
    */

    echo $allCookies['testing.dots'];
?>