"عِنْد سيث تَنّورة."
Translation:Seth has a skirt.
If you mention the possessor first (Seth) then you have to add a possessive suffix on (3ind) to refer back to (Seth), and it becomes (3indahu) - for a female that would be (3indaha). Otherwise, you can put the article first (3ind) and then the possessor (Seth) to make it simple. The article (3ind) means (at), and there is another article but I don't see it used here in Duolingo, probably for simplicity.