The default .bash_profile I accidentally deleted the contents of .bash_profile in my new Macbook Air and want the default settings that comes with macOS Sierra. 

Can anyone just copy/paste their .bash_profile that hasn't been edited?
The default .bash_profile is empty, as the file doesn't exist in /System/Library/User Template. Anything you've deleted would be something you (or software you installed) has added, so it's not possible to say what that would be. Copying .bash_profile from elsewhere would depend on the environment being configured in such a similar way as where you're copying it from.