Hello! LO Lo lo lo lo

YO! YO Yo yo yo yo

turns the soundproofing on

Okay now that's better.

I'm an absolute beginner and I have a question! What is the feminine equivalent of a-t-il?

In a magazine, I have the line lui demanda-t-il, which comes after a male character asks a question from his sister, so it prolly should mean he asked her or something. But I can't parse it.

Il is the subject here. It comes after the verb in those small interpolated clauses.

If the subject were female you'd say “lui demanda-t-elle”.

Lui is a pronoun for an indirect object (the person you ask from) and it's lui for both genders.

The -t- is a phonetic artifact that is used when the subject appears after the verb to prevent a syllable break between two vowels (called “hiatus”).

@StéphaneGimenez Great answer. Many thanks.