Are J1 visa holders eligible for this years stimulus check ($600)?

If you are considered a resident alien for tax purposes, and as such file a form 1040 because you qualify under the substantial presence test, then you should qualify for a stimulus check. You can apply for it on your 2020 tax return in TurboTax as follows:

When you prepare your tax return for 2020 in TurboTax, you will be prompted to enter how much you received for your stimulus and then the program will calculate the amount of stimulus due you based on your income, number of dependents and payments already received. If any additional stimulus is due you, it will be used to reduce your 2020 income tax liability, and the balance will be refunded to you.

You will see the options when you are done entering your tax information and proceed to the review process.