Redirect these 404 to homepage. And also remove them form index via GWT.

Redirect these 404 to homepage.

Redirect that URL to existing UEL with htaccess file.

Write this kind of code in your htaccess file -

RewriteEngine On
Redirect 302 /cdn-cgi/nexp/dokv=88e434a982/ http://www.domain.com/abc.html

Then upload it and fetch as google in webmaster tool, GWT display that URL as a redirected.

Remember that if you want to passes link juice then use redirect 301 (permanent redirect) and 302 (temporary redirect) that not pass link juice.

Redirect those pages back to home page or make a awesome 404 page linking back to other pages of your website.

You should redirect 404 not found error pages at relevant category page or home page, after doing this "mark as fixed" in Google webmaster tool.

Some website errors if not solved, like the 404 page not found errors, are very bad for SEO. If you have added your website to Google Webmaster Tools, you will find a section list possible crawl errors. Google bot crawls your websites or blogs regularly. Any crawl or access errors detected by Google will show up there.

To fix a 404 error is easy. First click on a URL displayed, you will get a pop up dialogue with two sub-tabs: Error Details and Linked from. Go to the Linked from tab, you will find what pages or sources linked to a not existing page on your website. If the web page did existing before and you made changes of its URL, it will cause this issue. In such case, you can simply redirect the old URL to the new one. For those unknown URLs, you may consider to direct them to similar page or the home page. If your business partners, clients, suppliers or link partners referred a lot of visitors to an false URL, you can also contact them to point to the correct URL.

Please don't redirect all 404 to home page. It is not the proper way to handle the 404.
First, redirect those to pages which consist similar kind of information.
and second, if you don't have such pages at all of it is impractical to do for huge number of pages then create a custom 404 error handling page where you can apologize to the visitor that the page you are looking is not exist. Then offer one or two options like link back to your home page or custom search to find similar kind of things in your website.

Redirect that page with htaccess file.

Write this code in htaccess file -

RewriteEngine On
Redirect 302 /cdn-cgi/nexp/dokv=88e434a982/ http://www.existingdomain.com/abc.html/php

Upload htaccess file in root directory.

Then allow "fetch as google". Your URL automatically redirect and display as a redirected.

Fix 404 Errors with Google Webmaster Tools

In the above link it is clearly explained about it. It is useful. Since 404 error is not good for SEO.