By the book, preferences file is automatic saved on the target system as a .bak file. It should be in your system folder>preferences>Logic preferences.bak. This file contain all your key commands. It is also advised to keep a copy of this file somewhere else, in a cd-rom or another hd. Of course one of these experts (Christian, Steve or Martin) will explain you better.
Key commands are stored in Home Folder/Library/Preferences/Logic/com.apple.logic.pro . Don't confuse this file with the "com.apple.logic.pro.plist" located in your preference folder.
You can make a copy of the "com.apple.logic.pro" on another drive for backup purposes or to export it on another computer. To import it back, use "Import Key Commands..." in the "Options" menu of the Key Commands window. When you import Key Commands into Logic, it will create automatically a backup of your older ones in a file named "com.apple.logic.bak" in the same folder.
The "Copy Key Commands to Clipboard" of the "Options" menu can also be useful. You can then paste your KC in a word processor for reference.