Not to be rude, but I WILL write in kanji because if you're going to learn Japanese, you'll need to know kanji. I WILL help you with the readings of them though.
Basically, you can say: 何をしていますか。(The kanji is read なに）
There are many other ways to say this, but this is a safe, polite way to say it until you understand politeness levels enough to use some more intimate expressions.
If you want to look up other similar expressions like this, I'd recommend using
www.alc.co.jp . You can type the search in English (ie What are you doing?) and you'll get multiple answers immediately, it'll be much more quicker than waiting for a response here and you'll get lots of variety.
Hope this helps.
