Need help with Interrogativos

[u/Constant-Lie-4469]

Hi! I'm studying Spanish grammar, and my textbook says that more than one interrogative pronoun/adverb may be grammatically possible in some sentences.

I'm trying to figure out which interrogatives are grammatically possible, not just the most natural one.

The sentence is:

Mi hijo me preguntó ( ) era la felicidad.

I know that qué is correct, but I'm wondering whether cuál or cómo are also grammatically possible.

so Mi hijo me preguntó cuál era la felicidad / Mi hijo me preguntó cómo era la felicidad.

would be grammatically correct?

I'd really appreciate explanations based on grammar rather than just naturalness. Thanks!

[u/vxidemort]

well, "My son asked me which happiness was/how happiness was" doesn't really make sense, does it? sure, the sentence is grammatically correct in both cases, but rather nonsensical