Hi there I'm not learning japanese that long but I think I'm able to answer your question: (きのう) ( なに) 昨日 は 何 を しました か。 But perhaps an answer from someone who is more skilled than I am would be better :D

i would say, in formal ways, きのうは　なにをしましたか？or きのうは　なにをしたんですか？ but if you wanna say it to your friends, more casual to say is きのう　なにしてたのー？　きのう　なにやってたー？. well, you might find it like," what were you doing yesterday?" but, to Japanese speakers（i mean to your friends), it sounds more natural to hear than きのうは　なにをしましたか？, i guess :)　good luck! :D

When talking about times such as today, yesterday, etc. you don't need は after it. You can just say きのう、。。。 I would probably say きのう、なにをしましたか。 or with friends, きのう、なにを*した*か。 (*plain/non-polite for casual conversation)