How can I see the details of the separate W2s from a previous year's (say 2018) tax return that I filed with Turbo Tax?

Individual W-2's are not listed that way on your tax return.

I NEED A COPY OF MY W-2  (or 1099)

TurboTax does not have a copy of your W-2—the Wage & Tax Statement—issued to you by your employer, (nor does TurboTax have copies of your 1099’s).   You should always save those documents for your own records. You could ask the employer(s) for copies or you can get a copy from Social Security (for a fee of $86).

If you saved a pdf of your completed tax return, the worksheets will show the W-2 information you entered, but not the actual W-2.

To get a copy of a W-2 from Social Security https://faq.ssa.gov/en-us/Topic/article/KA-02501

https://www.irs.gov/help-resources/tools-faqs/faqs-for-individuals/frequently-asked-tax-questions-answers/irs-procedures/transcript-or-copy-of-form-w-2/transcript-or-copy-of-form-w-2

You can get a wage and income transcript from the IRS:  It will not show the actual W-2, 1099’s, etc, but will show the income information the IRS received.  It will not, however, show your state information. It will only show the federal information.

https://www.irs.gov/individuals/get-transcript

https://ttlc.intuit.com/questions/2561916-how-can-i-get-a-copy-of-my-w-2

I need to be able to copy my tax return from 2018 can I download that through TurboTax please help