How to use youtube-dl --cookies
Once you get the cookies, you only need to run 
youtube-dl --cookies /pathtocookiefile  

If you use Chrome and accept third-party plugins to read your cookies.
Just try this cookie.txt,open the youtube then click cookie.txt plugin.
One more click ,you can download the cookie file for one tab or all.
 

If you want do it manual in Chrome. F12 >  Application > Storage > Cookies.
You need convert cookie list to Netscape format cookies file

#domain          HTTP/Secure    Expires      Name Value  
.youtube.com     TRUE/FALSE    1548523767    GPS    1