powieść is feminine.
Why is it feminine?
it's the verb that decides the case of a noun or adjective+noun group, czytam requires Accusative, so both will be in Acc. forms.
Czytam ciekawą powieść.
I am going to post a few examples of my exercise to clarify my task.
E1. Oglądam ................ [stara fotografia]
stara fotografia = feminine, so:
Oglądam starą fotografięE2. Czy masz ............. [mój klucz]
Mój klucz is masc/inanimate so remains nominative, so:
Czy masz mój kluczE3. Czy masz .................[młodszy brat]
młodszy brat is masc/animate, so:
Czy masz młodszego brataI hope this will explain my task better.
I have not been instructed on using the verb to determine the case but to use the noun and adjective, as above.