1. Via a direct link. Copy the YouTube video's URL, open Videos → Add video (in the upper right corner) → Add from a different website → paste the link and click Save.
2. Under YouTube videos click on Share → VK → check Add to My Videos and click Send. If you cannot find the VK button there, then you need to change your location to Russia at the bottom of the website.
3. Simply post the video’s URL on your wall and it’ll be added automatically.