How can I check my YouTube messages on my touch ?

Im sure you can't check youtube messages on the youtube app or on youtube mobile. However at the bottom of the youtube mobile page it should say go to desktop or full version. Then you can access all features of youtube.

The above post is correct... The YouTube app only allows you to access the videos on the store and it ensures that it can play all videos that users post to the site.

All other advanced functions must go through the actual webpage.

Also just to note that the subscription and login features to YouTube just came in with the 3.0 software. So in the future you may see some of these features, in addition you can ask for a feature like this to be included in future releases by posting that request here:

http://www.apple.com/feedback/ipodtouch.html

Hope that helps!