what is the shortcut for centering the cursor in the timeline in Premiere Pro CS6?
(I can not find it e.g. here: http://helpx.adobe.com/de/premiere-pro/using/default-keyboard-shortcuts.html)
I don't think there is one.
Nope. No such command. Your best bet--if you're decent at timecode math--would be to divide sequence duration by 2 and type that value in the Playhead Position timecode control in the Program Monitor or Timeline. (For those not familiar with the interactive nature of that control, typing any valid timecode there causes the playhead to jump there.)
Of course, if the sequence has a non-zero start timecode, then you have to add that offset.