How do I view my 1040 for 2018 in progress?

If you have not filed the 2018 tax return then just sign onto your online account and continue your tax return.

To access your current year online tax return sign onto the TurboTax website with the User ID you used to create the account - https://myturbotax.intuit.com/

Or are you asking how to preview the actual Form 1040 while preparing your online return?   There are 2 options.

You can view the Form 1040 for free at any time during preparation prior to paying and filing.  Here's how:

• Open your return, and in the left menu column, choose TAX TOOLS, then choose TOOLS.
• In the Tools window, choose View Tax Summary.
• When the Tax Summary opens, look in the left menu column and choose Preview My 1040.
• That will show you the Form 1040 Worksheet and Schedules 1-6.

Or you can pay in advance to view/print the Form 1040 and all forms and any worksheets prior to filing.  Here's how:

• Open your return, and in the left menu column, choose Tax Tools, then Print Center.
• Then choose "Print/save/preview this year's return."
• On the next screen choose to "Pay now".
• The next screen should be an Order Summary.  Review that, and if all is OK, click Continue.
• It should then prompt you for payment by credit or debit card.  The screen only says "credit card", but it will take a debit card.

NOTE:  If it should offer you the option to "pay later" out of the Federal refund, that can't be used for this purpose.  You will need to pay now by credit/debit card in order to download/print prior to filing.