got a 1099-k from ebay. Schedule 1 form 1040 right at the top lets you claim items at a loss. Where in turbotax can I claim a loss?

Personal losses are not deductible.  The line on Form 1040 Schedule 1 for personal losses is informational only, not a place you can claim a personal loss. See your previous post for instructions to report the 1099-K: 1099-K form from personal items