it's like "do" and "make" difference set phrases only as for 工作 it will be 做工作

For this case, you should express your idea as "你做什么工作?". For details: 1. “作” is much more formal than “做”. Best illustration is that almost every possible CHENGYU contain "作" rather than "做". e.g. 当牛作马、敢作敢当、敢作敢为、故作高深、胡作非为、矫揉造作、苦中作乐、弄虚作假、述而不作、无恶不作、为非作歹、为虎作伥、为人作嫁、惺惺作态、寻欢作乐、以身作则、自作聪明、自作多情、自作自受、作恶多端、作法自毙、作壁上观、作奸犯科、作茧自缚、作如是观、作善降祥、作威作福 2. Usually, "做" followed by a none describes a certain action, thus it is concrete. However, "作" sometimes is abstract. It will not related to a certain action. E.g. 作用 (function)、作风 (work style) 3. When consider describing a two-word verb, "作" should be used. But, when consider describing a two-word none, "做" should be used. E.g. 作报告、作测试、作比较、作补充、作变动 做工程、做功课、做记号、做家务、做课题 4. However, in some cases, there is no significant difference, you can use both at the same time. For more details, pls check out (Sorry, but it is written in Chinese): Ref. http://zhidao.baidu.com/question/13345737

“你做什么工作？” 做 can be followed by lots of things like "做功课、做记号、做家务、做作业、做事情, really similar to DO 作 as a verb, it seems to me the most important one is "作为”=AS also u can say 作报告、作测试、作比较、作补充 etc. but i think if u use "做" instead, it still strike people as right

I agree with Mekey, when you simply compare those two characters, quite often, 做 would be used as a verb, and 作 is an adv. but you should know the meaning of a compound word is different from the separate meanings of its components. and a character may have several different meanings and is often more like a syllable in English. sooo, if you wanna learn more, you should ask me, lol....

a very good example : 做作业 做：verb 作：nom