How to add Cookie Magento 2?

IMO the best approach would be to create a class to wrap the cookie creation and then just use it where you want.

The Cookie Class

{Vendor}/{Module}/Cookie/Example.php

<?php 

namespace Vendor\Module\Cookie;

use Magento\Framework\Stdlib\CookieManagerInterface;
use Magento\Framework\Stdlib\Cookie\CookieMetadataFactory;
use Magento\Framework\Session\SessionManagerInterface;

class Example
{
    /**
     * Name of cookie that holds private content version
     */
    const COOKIE_NAME = 'example';

    /**
     * CookieManager
     *
     * @var CookieManagerInterface
     */
    private $cookieManager;

    /**
     * @var CookieMetadataFactory
     */
    private $cookieMetadataFactory;

    /**
     * @var SessionManagerInterface
     */
    private $sessionManager;

    /**
     * @param CookieManagerInterface $cookieManager
     * @param CookieMetadataFactory $cookieMetadataFactory
     * @param SessionManagerInterface $sessionManager
     */
    public function __construct(
        CookieManagerInterface $cookieManager,
        CookieMetadataFactory $cookieMetadataFactory,
        SessionManagerInterface $sessionManager
    ) {
        $this->cookieManager = $cookieManager;
        $this->cookieMetadataFactory = $cookieMetadataFactory;
        $this->sessionManager = $sessionManager;
    }

    /**
     * Get form key cookie
     *
     * @return string
     */
    public function get()
    {
        return $this->cookieManager->getCookie(self::COOKIE_NAME);
    }

    /**
     * @param string $value
     * @param int $duration
     * @return void
     */
    public function set($value, $duration = 86400)
    {
        $metadata = $this->cookieMetadataFactory
            ->createPublicCookieMetadata()
            ->setDuration($duration)
            ->setPath($this->sessionManager->getCookiePath())
            ->setDomain($this->sessionManager->getCookieDomain());

        $this->cookieManager->setPublicCookie(
            self::COOKIE_NAME,
            $value,
            $metadata
        );
    }

    /**
     * @return void
     */
    public function delete()
    {
        $metadata = $this->cookieMetadataFactory
            ->createPublicCookieMetadata()
            ->setDuration(0)
            ->setPath($this->sessionManager->getCookiePath())
            ->setDomain($this->sessionManager->getCookieDomain());

        $this->cookieManager->deleteCookie(
            self::COOKIE_NAME,
            $metadata
        );
    }
}

This example was based on Magento\Framework\App\PageCache\FormKey and represent a single cookie with name "example"

If you want to add some custom properties to the $metadata (PublicCookieMetadata) as change the path,http_only, etc you should refactor the set() and/or delete() method(s).

How to use it

You can access that class simply using the Object Manager in almost anywhere (Ugly Approach):

$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$objectManager->get('Vendor\Module\Cookie\Example')
    ->set('value', 3600);

Depending "where" you need to create the cookie you can take a look at the constructor of your class maybe you already have an Object manager there, if not you can also inject it in the constructor.