I am a Pakistani student in Germany with a Schengen visa. I need to visit the UK. What would be the (short stay) visa requirements?
Your Schengen visa isn't valid for the UK although it might make it more likely that you'll be granted a UK visa.
You can check the UK government web site to determine what visa you might require, if any.
In your case, as a Pakistani citizen you will probably need a Standard Visitor Visa: the web site I linked to will tell exactly what you need if your needs differ.
You can apply for a visa through TLSContact, who have centres in Munich, Dusseldorf and Berlin.