"What is the nature of this relationship?"
Translation:Jaki jest charakter tego związku?
Yeah... my first thought is "why are you suddenly writing about sex". No, that does not look like a good idea.
Just to specify, "stosunek" can mean "❤❤❤❤❤❤❤❤❤❤❤", and unless you specify "stosunek between what and what", that would probably be the first assumption.
Basically, even in English you have something like an 'adjectival what', although you don't really see it, because there's no difference between this one and the basic one. This is an 'adjectival what'. You expect, or at least can expect, a more descriptive answer.
I don't know if it's helpful, this was always one of the most difficult questions for me.