I want to see my 2024 AGI in preparation for mitigating my underpayment penalty. How can I see this?

You can view your Form 1040 plus Schedules 1, 2 and 3 at any time using the online editions. Click on Tax Tools on the left side of the online program screen. Click on Tools. Click on View Tax Summary. Click on Preview my 1040 on the left side of the screen.

Before filing,  You can preview the 1040 or print the whole return

https://ttlc.intuit.com/community/accessing/help/how-do-i-preview-my-turbotax-online-return-before-filing/00/26160

PREVIEW 1040

https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/preview-turbotax-online-return-filing/L77WCkvnu_US_en_US?uid=m681fkhr

Do you need your 2024 AGI or the 2023 AGI? If you have a penalty on 1940 line 38…..

You might be able to eliminate it or at least reduce it.  You can go to Federal Taxes tab or Personal tab, under Other Tax Situations and select Start by the Underpayment Penalties. You will answer a series of questions that may reduce or eliminate the penalty. Or you can elect to have the IRS figure the penalty for you.  It's form 2210.

It's under

Federal or Personal (for Home & Business Desktop)

Other Tax Situations

Additional Tax Payments

Underpayment Penalties - Click the Start or update button

If you have the desktop program you can switch to Forms Mode (click forms in the upper right (left for Mac)) and open the 2210 form.  If the 2210 doesn't show up in the left column, click on Open Forms at the top of the left column.  Type 2210 in the search box and open the 2210 form.  Check box C to let the IRS calculate it.