What mutations are needed for a particular trait (e.g. wings) to arise?

firstly you need to be clear where you start from .. feathers where around before birds , very light bone structure was a round before birds , modified forelimb structure was around before birds , the wishbone chest structure also may predate birds ...and all of these features had being evoling over a vast time scale .birds are a result of the accumilation of such features and suitible enviroment for favour such development .to map the mutations that gave rise to each feature would firstly need a full mapping of the bird DNA , and given the current range of bird s where would you start ?If you are looking for a step by step mutation map , you need to remember a mutation may occur ages before it becomes a seletcted trait within the population , it may sit dorment until a new enviromental pressure is applied .as no one , as yet , a can travel back in time it is a lack of DNA samples from the vast timeline , that would make any mutation map difficult .Note there are no errors due to mutation .. because there is no plan for mutation ... some will be leathal , all others only time will tell if they prove to be benifit or harm .
Further ther will be some mutations which may appear to have nothing to do with a line evoling into birds , but may have played a vital roll at a certain time point , ie desiease resistance to a plauge which cut down the compitition and opened up a space for the proto birds to exploite with low pressure .

a very non stupided question ...the whole point is its a dynamic , interedendant system that every creature lives in , the whole system IS a filter , and getting through is the only measure of good / bad / indifferentan single mutation to a creature can be benificial and harmful and neutral and a given point in that creatures liniage .eg a creture may mutate so that it hasd a dark blue spot on its tail , seem s to have no effect on creaturetime passes , a new periditor has evoled near by that happens to have eye that are very good at spotting deep blue , and so this preiditor nearly kills off our creature by hunting .more time passes and the pressure from the preiditor has selected those creatures in the population with that can feed in the darker hours of the day around dawn and dusk , this population has sleceted for vision that sees better in the dark , now this so happens that for individuals that have good low light vision the deep blue spot is a good way spotting fellow creatures ands becomes important trait in finding a mate , and hence breeding .thus we have a mutation being all 3 types over a prolonged period , set along side changes to perdation , enviroment and breeding condistions .it has been said if you rewound evolution and re run it would you get the same results ... and the answer given is maybe not .. you would end up with a lot the same but the steps and stages could be diffrent .as the measure of benifit / harm can only be seen after the creaturte has survived or died out , hindsight is the only tool .