Where do I fill out the W2 form from Dollar General?

Ask your manager.

BTW, a W-2 would not be sent by e-mail as it's not secure. It may be available on a secure website IF you opted out of receiving a paper W-2 in the mail. If you didn't opt out, they must mail it to your last know address on file.

request a duplicate from the employer

If you are gong to fill it out, it isn't a W-2. A W-2 is a report of earnings for last year. Did you mean a W-4, which is the form you fill out when you are hired (and change when you need to) to give information so payroll can withhold taxes properly?

Check your e-mail Trash / Deleted folder, and then Move it back to your Inbox.

Search your email. Some keep them on their systems forever and even deleted emails will show up in a search. Other than that, if the company has a website that your pick up your paystubs from, the form may be there.

You don't do anything to your W-2

It's called "email them" or "phone them", Einstein. WAIT .... I'll pull it out of my assss for you!