Can I receive the Retirement Savings Contribution credit. I only contributed to my 401K through Palmetto Goodwill. See box 12 on W-2 form.

[aww2018]

Or is the 401K outside of my job the only way to receive the credit?

[dmertz]

TurboTax automatically includes your 401(k) elective deferrals and Roth contributions shown in box 12 of your W-2 in determining this credit.

[Opus 17]

You can't have a 401(k) "outside" your job, a 401(k) is exclusively an employer-sponsored plan.  You can have an IRA, but an IRA is not a 401(k).  Your 401(k) should be reported on your W-2 and Turbotax will take the info from that. 

The retirement savings credit has a pretty low income phase-out, and you can't be someone else's dependent to get it. 

https://www.irs.gov/retirement-plans/plan-participant-employee/retirement-savings-contributions-save...

https://www.irs.gov/newsroom/get-credit-for-retirement-savings-contributions