i cant find my serial number to logic pro 9 to activate i got a new computer

If you bought the Boxed version of Logic then you have two basic choices....

1) If you still have your old comoputer and Logic Studio 2/Logic Pro 9 is installed on it.. Open up Logic and go to the Logic Pro menu option and choose About Logic and you will find your serial there (Assuming you bought the full version of Logic 9 DVD) If you bought the upgrade version of Logic Pro 9 then you will also need your Logic 8 serial as well..... which can be obtained the same way if you retained the original copy of Logic 8 on your old Mac.

2) Use the following form to contact Apple get issued a replacement serial for Logic Pro 9

https://ssl.apple.com/support/proapps/serialnumbers/

If you bought your full version of Logic 9 from the App Store you don't need a serial (as it uses your existing Apple ID and Password to authenticate) and can simply open the App Store App on your new Mac, navigate to the purchased tab and redownload Logic 9 from there.