We had an expert put in the key code to access our wireless system. Short of asking the nerd how can I find it?

Hmm by wireless I am assuming wireless internet
Possibly you have a router if using wireless?
Then the router's instruction booklet will tell you how you can change password
I believe there is no way to read the old password (except by hacking or cracking)
So you have to reset the router and redo all you configuration and set new password

What is my key code