Was the 2016 return prepared in Online TurboTax (website version?) If prepared in desktop software (CD/download), the *.tax2016 data file and any PDFs would be stored locally on your computer or external media.
If the 2016 return was prepared online, log in and go to the Tax Home page. It
may already open by default on the Tax Home page. If not, you can
click Tax Home in the left menu column. Then on the Tax Home page
scroll down to "Your Tax Returns & Documents". Click on that line or on the word "Show" to expand that topic Then you should see a list of
prior tax years. Click on the one you need.
If you do that, but
find no evidence of the 2016 return, then you likely have multiple
accounts and signed into the wrong one. To
get a list of your User IDs and recover account access, you can use the
tool at the link below.
Try using your phone number first. After
that, if necessary, then run the tool on your email address(es) you can
access.
NOTE: Before running the
account recovery tool below, log out of all Intuit accounts including
this user forum, or you might end up in a loop. Then clear your browser
Internet cache, close your browser, then reopen it, and go to the link
below. You may wish to copy this link so you can paste it into the new browser session.
https://myturbotax.intuit.com/account-recoveryIf
still no luck after running that on your phone number and email
address(es), then go back to the tool again, but
this time leave the data field blank, and choose the
small blue link that says
"Try something else", and it will look you up by SSN and other parameters.