"Konys prūbres ēngenkys issa?"

Translation: Is that apple tasty?

[HinjakuHinjaku]

"Is that a tasty apple" was marked incorrect. Why is it wrong?

[xPsGoDWh]

Because "that", in this case, modifies the noun, so it needs to be "that apple". "Is that tasty apple?" would be an incomplete sentence, and so it needs to be "Is that apple tasty?"

If "that" was an independent element of the sentence, it would be "kony", not "konys".

[HinjakuHinjaku]

Thanks for answering. So the meaning depends on the ending of kony.

[xPsGoDWh]

Not quite. It depends on the ending of "kon*". The -y ending is a noun ending (like in Dovaogeedy). "Konys" is a declined form of "kona" (-a being an adjective ending).

[HinjakuHinjaku]

Thanks for answering. Are all words ending with y are nouns?

Also are there other endings that tell about which part of a sentence a word is?

[xPsGoDWh]

IIrc, yes, all the words ending in -y are nouns (lunar nouns, to be precise). It's not quite as easy with most of the other endings, since the corresponding adjectives often take the same ending when declined. But -illa is a noun ending as well (aquatic, in this case). Mind you, this is all just the nominative singular, if the words are different parts of the sentence or a different number, they'll have different endings.