Japanese learning

Question using interrogatives are marked by particle が (ga) not は(wa)

なに、だれ、いつ、どこ are marked by particle が because the speaker is asking for new information

なにがいいですか? nani ga ii desuka? What is good? ( = what do you want?)

だれがいいですか? dare ga ii desuka? Who is good? ( = who do you want?)

いつがいいですか? itsu ga ii desuka? When is good? ( = when do you want?)

どこがいいですか?doko ga ii desuka? Where is good? ( = where do you want?)