I don't think that you can see it on the router. Where you can see it on the client computer depends upon the operating system and driver software. For example, in Vista if you open up the Network and Connections center and click on the "Status" of the wireless connection, it will pop up a dialog box showing a connection speed.
Take care, though. That type of software speed estimate is subject to errors. The best way to estimate the actual speed is to do a file transfer from memory. I believe that there are downloadable utilities available online to do this. Unfortunately I am not familiar with any of them to make a recommendation. Do a search and you should find some.
The issue with just doing something like a computer to computer file copy to estimate network speed is that a fast network can outpace a slow hard drive. If you chose to just time a file copy to estimate speed, then you will know that your connection is at least that fast and possibly faster.