Well, according to my grammar book, you cannot place に beside 今日 or anything like that (ashita, kyou, getsuyoubi, etc). Why does も replace を? I thought 何も was a full word. Please explain it to me. Again, my grammar book says I can't place に beside 今晩. 今晩は means Good Evening. 今晩 means tonight. ??? Now I'm confused.

I'm not native Japanese person nor am I fluent in the language. I am also learning Japanese. I might have phrased these sentences as follows: A: 今日は何をしましたか。 Literal translation: As for today, what did (you) do? That "you" is the target of the question is obvious because "you" is the person being spoken to. あなた can be and it is probably more natural to omit. 今日は can parhaps be replaces with 今日に although I think that might not be as natural. B: 何もしなかった。／何もしませんでした。 Literal translation: (I) did nothing. I'm not sure, but I believe も replaces を. A: 今晩は何をしますか。 Literal translation: As for this evening, what will (you) do? Again は might be replaces with に as in the first sentence. B: 昨日のあなたの家でいるの時に何を食べましたか。 Literal translation: At the time when (I) was at your house yesterday, what did (you) eat? I'm not sure about whether this one is correct. Again, that "I" was the one at "your" house should be obvious from content. Although, if "I" was there, shouldn't "I" already know. I think the question I've written is gramatically correct, but it makes little semantic sense.