Enable Marvin Mode
Marvin Mode is not only for cheating. It's also a tool which can help you change items, quests e.t.c. You can find everything you want there. But to use this "mode" you have to enable it first because it's locked (somehow). That's
what i'll show you on this tutorial.
Step 1 : Go to (default) C:\Program Files\Gothic III\Ini and open the "ge3.ini"
Step 2 :
Find the line Testmode
Step 3 :
Change TestMode from false to true- just write true where false is.
Step 4 : Run the game. In the game press "~"
Step 5  :The console should show up.
The console is enabled but there is a graphical problem , what's the problem?
Do not get dissapointed. In the most users (mine too) there is this problem.  You just have to do the following to fix it:
Step 1  : Download G3Pak   
Step 2  : Run the G3Pak program go "file>open-GothicIII>Data>_compiledImage.pak"
Step 3  : Press "extract dir"
Step 4  : Run the game. The console will be working fine now.

(Maybe there is also another way to do it. Just go to GothicIII\Data and create a folder named copmiledImage and then another
empty folder in it called Intern.)
Cheats "Give" commands
Thanks to World of Gothic