Then it would have to be: Co to jest "efekt"? or better: Co to znaczy "efekt"?
Without 'to', the sentence is just wrong, I'm afraid.
I think kenney1321 was asking about the parallel of "What is the effect," and the word "what," Polish co, since the translation uses jaki which translates as "which." This is confusing to English-speakers because we use "what" here. If you translate literally Co jest efekt, it doesn't work.
I'd say that "which" translates to "który", as it suggests a finite set of answers (option A, option B, option C).
I'd also say, but that is only an opinion/interpretation, that "what" can be a bit... adjectival someone. And it's this 'adjectival' what that translates to "który".
"Co jest efektem?" would be a valid sentence, but anyway a less natural one than "Jaki jest efekt?"
I am writing to kenney1321 actually but couldnt answer him. I think that you should think jaki like something like "what kind of". Generaly co goes to nouns and jaki to adjectives. Example. 1. - co to jest? to jest samochód. 2. Jaki samochód? Czerwony/syzbki/stary (etc) samochód.
I get it now! I actually think we have a similar difference in my own language (danish). But I guess I often forget to compare it to that instead of english..
Allright, thanks for the answers! Could you specify the difference between co and Jaki a little more, so I'd know when to use each of them?
So the way I'm understanding it is that what/co is a noun in Polish, and
what/jaki-jaka-jakie is adjectival, describing a noun such as Jaki jest efekt
In this context, I'd say that "What's the result?" sounds more like normal English than "effect". At least it should be allowed.