"Moja córka jest studentką."

Translation: My daughter is a student.

[shirel.tai]

Why student is written with an ą ?

[ngfio]

Because the case you have to use in this sentence is not the nominative. "Moja córka to studentka", but "Moja córka jest studentką", see https://en.wiktionary.org/wiki/studentka#Polish.

[JaniceSchl1]

Instrumental yes?

[BenYoung84]

Yes

[VcR9JJ27]

Zła intonacja lektora - jak w zdaniu pytającym!

[Gabriel375386]

Why can't we say "My daughter is student" instead of "a student"

[BenYoung84]

English is very consistent about putting an article in front of nouns, so writing "My daughter is a student" follows standard English rules and omitting the "a" is incorrect.

[HiranNagar]

When describing a persons profession or relationship instrumental case is used and the case ending is respectedly implemented (ą).

[alik1989]

I'm afraid that's just inaccurate. Every sentence which is built as "[noun] jest/są [noun]" puts one noun in the instrumental case. And the -ą ending is only for feminine nouns, as well as masculine nouns that end in -a. Other masculine and neuter nouns get an -(i)em ending and plural nouns get an -ami ending.

[HiranNagar]

Thanks for the correction.