Is there any way that a user can route a question or notify other user about it? For example I found a question that I know that certain user can answer, is there a way that I can notify this user about this quesio
No, there is no feature on the site that allows you to do this.
Put yourself in the other user's shoes. Do you want anyone and everyone to be able to spam you with links to questions? I didn't think so.
The Stack Exchange sites are not social networks nor forums. There is no support for sending private messages to other users. That's completely by design and unlikely to change. (And if it ever does, you'll see a whole bunch of us leave. I'll be first. Form a line—single-file, please. No shoving.)
Of course, if a user chooses to disclose his/her contact information in their profile, you can use this to contact them. Or if you both hang out in the same chat rooms, you could post a link to the question.
No. This functionality is not available.
Further, I don't believe this will ever happen as it's designed to be a community website, not a message board from one user to another.