Ok. Let me first go through what you have written. The first two are he same sentence lol. 1) 你在干什么呢？ - what are you doing 2) 你在干什么呢？- what are you doing I think you want to know what the difference is when you add 呢 and when you don't. There is almost no difference, just a slight difference in tone. 3) 你在做什么？- this I suppose is ever more slightly more formal than 幹什麼. 做 is a more formal way of saying "to do" 4) 你做什么着？- I have never ever heard anyone say this 5) 你做什么吗？- this is a bit wrong. If you want to know what someone is doing, I hear people say the following: 你在做什麼？ 你在幹嘛？ 你在幹啥？ 幹嘛去？(this is Beijing dialect) Laurence

既然他们都已经回答你了。那我就抛开你的设问来回答。"what are you doing (now)？" 我一般说：①你（正）在做什么呢？②你正在干什么呢？ 你问这个问题的时候，语气tone很重要。 1) 你在干什么？ 3) 你在做什么？ 如果你的语气较硬，这2句话听起来有点凶。语气缓和一点也还好。 2) 你在干什么呢？ okay 4) 你做什么着？5) 你做什么吗？ wrong！！ “着”and “吗” 用在这里不对。 In addition，I think you'd better use "做“ because sometimes “干” means “fuck”.

First, the fourth is grammatically incorrect. The fifth is grammatically correct, but sounds weird and it means "Do you do something?" Now the first and the third both are correct, and 呢 is used to soften the tone. However, in this context, 干 carries a slightly stronger tone than 做, so the first one is more like questioning and the third one is more like inquiring and it's more common that the optional 呢 appears in the third sentence.

1) 你在干什么呢？ 2) 你在干什么呢？ What are you doing?// What the hell are you doing? or more colloquial, 你（在）干啥（呢）？ 3) 你在做什么？ In mandarin, this probably means ' what are you making'? 4) 你做什么着？ ✘ 5) 你做什么吗？ （✘） Are you making something/ Are you doing something? This sentence is unlikely about what you're trying to say. All by itself it will be confusing but will fit some specific contexts very well. ---- If you live in China, you'll find find that the northern people use more 干，and the southern more 做，although both are understandable.