What kind of knife are you looking for? Should it be a fixed blade or a folder? How much do you want to spend? And last but not least: Which part of Germany will you visit?
If you're visting the south of Germany (Bavaria) you could buy a fixed blade called 'Trachtenmesser' at a local hunting store. A Trachtenmesser is a hunting knife wich is part of the bavarian traditional outfit. Its also called 'Nicker' in German. Have a look at these Nickers:
However, if you prefer a folder to a fixed blade you might consider bringing a 'Loewenmesser' back home. These are mostly traditional slipjoints made from carbon steel. They will hold their edge for a long time and can be sharpened easily but will rust if not properly maintained. They are rather cheap but very useful. Loewenmesser can be found here:
A catalogue can be downloaded here:
Loewenmesser are made in Solingen, the traditional cutlery center of Germany. It's located in the west of Germany. Another renowned manufactor from Solingen is Boker. Right now they offer some interesting reissues of German military knives like the German trench knife:
They also make some very nice folders and slipjoints. Especially the products offered by the Messermanufactur of Boker are high quality knives. The only obstacle to buying a Boker knife might be the fact that they are fairly popular in the US, too, and can be easily bought online from Boker USA. On the the other hand this surely will become an advantage if at some time or the other the need to contact their customer service should occur. Boker has a forum here, too.
Let me add something else. If you travel as soon as next week prepare to meet some difficulties as public transportion likely will be on strike in large parts of Germany. Trains and airports will be affected everywhere. In Berlin all public transpotation will come to a standstill. This is really a nuisance. Neververtheless I wish you a good trip.