I invested $12,000 in a restaurant startup and it failed and lost the entire investment. Can I claim this and if so where?

Yes, you can claim the $12,000 you lost on your restaurant investment. You will report the sale in the same section in which you report stock and other investment sales.  To Enter in TurboTax: 

• Type "Investment sales" in the search window and click Enter
• Click on "Jump to Investment sales"
• On the page with "Did you have investment sales in 2023?"  Answer Yes
• Answer No to "Did you cave crypto income or losses in 2023?" 
• Skip the import sections and click on Enter another way
• On the screen with OK, let's start with one investment type, click on "Other"
• Answer No to "Did you get a 1099-B..."
• Enter the name of the person or entity that brokered the sale (you can leave this blank)
• On the "Now enter one sale for [description]" Indicate "Other" and give a description like "Restaurant Start-up".
• The interview will walk you through entering the details of the sale

I would enter the same value for proceeds and fair market value.  

Thank you!  One clarification.  I was not the owner of the restaurant.  I gave the $$ to the owner and he was supposed to pay a certain share of the monthly profits, but we never got anything and then the restaurant defaulted.  Does your guidance still apply under this scenario?

Yes, it would still be the same.  It would be similar to purchasing stock that became worthless.