How can I watch slowed down Youtube videos in iPad?
That tutorial on slowing down YouTube videos was made in iOS 5 with the older YouTube app. You probably have iOS 6 and are using the YouTube website or the YouTube app released by Google more recently.

Both the web app and the YouTube app no longer play videos with the QuickTime player with those controls. The only thing that still uses that interface is the YouTube app on the iPhone. I suppose you can try experimenting with other third-party YouTube video viewers, one of those may use QuickTime for playback, but I don't have experience with them.

By the way, I don't know how useful that video will be even slowed down, and there are a lot of great Blender tutorials out there if you look.

EDIT: Actually, embedded YouTube videos will use that player, so you just have to embed the video on a web page and then browse to that page on the iPad.