Currently I have to open Team Explorer and click on Source Control Explorer
as below snapshot.
I do this very often and need a hotkey for that.
What
You can use Ctrl+0,P to open the Pending Changes Window.
You can find all the shortcuts for team Explorer on this blog: http://blogs.msdn.com/b/buckh/archive/2012/06/06/team-explorer-2012-keyboard-shortcuts.aspx
Update:
In Visual Studio 2013 Ctrl+0,P
doesn't seem to work to open Pending Changes, but you can use Alt-V,E,H
or configure a custom shortcut in the menu Tools/Options/Environment/Keyboard
.