"Wer macht was?" is very economical. Actually, it's two questions and short for: 'What's to be done? And who will do it?' "Wer macht was?" ist sehr sparsam. Eigentlich sind es zwei Fragen. Die Kurzform für: "Was muss getan (/gemacht) werden? Und wer tut (/macht) es?" If "was" (=what) means "etwas" (=something) the sentence would say 'Who will be doing something?' Preparing a cake for a birthday party. Or: 'Who will volunteer?' Who's the first one to say something? Wenn "was" "etwas"(/irgendetwas) bedeutet, dann ist die Aussage des Satzes "Wer macht etwas?" Wer MACHT einen Kuchen für eine Geburtstagsparty? Oder: "Gibt es einen Freiwilligen?" Wer wird zuerst (/als Erster) etwas sagen? Spoken slowly, in most cases it will be the first option. "WER macht WAS?"

Unfortunately this sentence is a bit out of context. Given like this I can imagine two different meanings, depending on which word has the stress... 1. *Wer* macht was? It means "*Who* is going to do something / going to contribute?". You could imagine saying this when your university / sports club is having an open day and the students / members are asked to contribute to this activity. 2. Wer macht *was*? It means "Who is going to do *what*?" In this situation a number of people already agreed to do something together but the tasks still have to be distributed. If you say more about the context it would be easier to give some more details. (Send me a message if you like!)