Here again... Why is this instrumental? Is this regular with 'być'? Or describing what you are? (jestem holenderką ?)
to identify (to name): TO (jest) (kto? co?) ciocia - Mianownik (Nominative)
to define: JESTEM (kim? czym?) ciocią - Narzędnik (Instrumental)
Yes, look at Tips and Notes: https://www.duolingo.com/skill/pl/Defining
I am a dutchman as well.
Which for a man is "Jestem Holendrem".
"Jestem wujka" is this right saying for "im an uncle" ?
"Wujka" is accusative/genitive, but here you would need the instrumental case.
Hence "Jestem wujkiem": https://en.wiktionary.org/wiki/wujek and 'show' the declension.
Why is it not "jestem ciotką"? According to wiki declension instrumental this would be correct...? https://en.wiktionary.org/wiki/ciotka
"Jestem ciotką" is actually an accepted answer; I just tested it.