HOW do i get a serial number for my lightroom program

If you purchased it online from Adobe then you should have the serial number in an email that you received after your verified order. If you log into your Adobe account you can also get detailed information about purchases and recovering serial numbers for products you own. If you no longer have your account information (email, name, password) you can contact Adobe support and they are usually very helpful with account recovery provided that you can verify your information.

If you purchased it retail the serial number should either be on the box near the barcode or on the DVD slipcase, usually inside under the disc or on the back of the DVD case.