If i have my serial number can I find out what Apple ID is used on it?

No. But the ID will be an email address that you may find here or by calling Apple Support: Contact Support.

For Problems With Your Apple ID

1. Forgot iCloud Password
2. Forgot Apple ID
3. iForgot Password - Apple ID
4. iForgot UserName - Apple ID
5. Apple ID - Apple Support
6. Manage your Apple ID primary, rescue, alternate, and notification email addresses
7. About your Apple ID email addresses
8. Get help with Apple ID

If you know the Apple ID or think you do and can login to it then you can see what devices are linked to that Apple ID under 'iCloud devices'. See iCloud: Manage your devices

However this works best if you have named the devices with a sufficiently descriptive name, if it was merely names 'My Macintosh' then that is not sufficiently descriptive, I use the serial number as part of the name.

The above instructions only work for devices capable of being logged in to iCloud so really old Macs will not be listed, but newer Macs, iOS devices and Apple TV and Apple Watch will be.