"Jaki/jaka/jakie" is a question about features/traits/qualities (which are often described by adjectives). "Co" which in this case would become "czym" (instrumental form) is a question about a noun.
I see that you're learning Spanish. "Co" and "jaki" work the exact same way as the Spanish "qué" and "cuál".
In Spanish, "qué" would imply that you want a definition. Let's say you don't know what a dog is, so you would ask "¿qué es un perro?" (what is a dog?) because you want a definition. This is when you would use "co" in Polish.
In Spanish, "cuál" would imply that you want general information. So, let's just say you are talking to someone you like and you want to get their number, you would ask "¿cuál es tu número?" (what is your number?). Here, you know what a [phone] number is and aren't asking for a definition. This is when you would use "jaki" in Polish.
Thank you so much! I have taken 5 years of Spanish and am nearly fluent, but never thought of making the comparison with qué and cuál. It makes so much more sense now.
You're welcome! Yeah, English somewhat lacks this grammatical nuance, so explaining how to use "co" and "jaki" with English is practically impossible.
Great explanation; clears up something that's been puzzling me for a while!
Seems to be, although more natural (but not accepted) would be "What are your results?" (even if there is only one result to be reported).