I was able to add a forgotten w2 without using an "amend" button bc it didn't populate for me. However, I don't have confirmation on if it was received. How can I know?

TurboTax will send you an e-mail notifying you whether or not your return(s) was accepted.  You can print and/or save a copy of your filed return and look it over to make sure the return includes your second W-2 income. Use the following instructions to do this. https://ttlc.intuit.com/replies/3401713