"Good morning, I am a doctor."

Translation: Dzień dobry, jestem lekarzem.

[MrBTTF]

"Dobre rano" is never said?

[Jellei]

"Never" is such a strong word... but yeah, I don't think I've ever heard it.

[Rozelyn-Claire]

Why is "Dzień dobry, ja jestem lekarzem" is wrong?

[Jellei]

It should have worked, it's accepted. But it puts an unusual emphasis on the subject, "ja" is totally redundant here.

[OndrejSaska]

Doktorka isn't a word?

[Jellei]

Not really. I mean, someone can use it, but rather as word play (a neologism) and totally colloquially, than being serious...

[Peter498186]

I find it really confusing when duolingo says "Another correct solution: Dzień dobry, jestem lekarką" and makes me think that I have not given the best solution. (I gave dzień dobry jestem lekarzem - the only thing I can see wrong is the "D".) For anyone else who comes here, lekarką is of course the instrumental for a female doctor.

[Jellei]

If it's "Another correct solution", then it means that your solution was correct. Both "lekarzem" and "lekarką" are considered equally correct here.