If you are using TurboTax Online, then unfortunately, you can't transfer returns between accounts. You can still give your son a PDF copy of his return for reference. This FAQ shows you how to find the PDF archive copy of your filed returns from previous years in TurboTax Online: https://turbotax.community.intuit.ca/community/navigating-turbotax/help/where-do-i-find-a-copy-of-my...

If you are using TurboTax CD/Download then you can give your son a copy of his tax files. By default, TurboTax CD/Download saves your tax files in a “TurboTax” folder in your “Documents” folder. You can copy the files from there onto an external drive and give them to him that way. He will need to download and install the software to open the files, though.

You can also give your son a PDF copy of his return. Here is how to save a PDF copy of your tax returns in TurboTax CD/Download: https://turbotax.community.intuit.ca/replies/2985586