This question is actually much more complex than you might think. A good estimate would be that professional sport athletes need around 0.6 to 0.8g of protein per pound of bodyweight, this can then be translated to around from 1.2g to around 1.4g of protein per kilogram of bodyweight.
However, the complexity lies in the fact that they actually do not need much more than that, regardless of them being a weight lifter or a marathon athlete. The reason for this is that here you're reaching the upper limit of protein utilization. For that reason, weightlifters who're consuming up to 3g of protein per kilogram of bodyweight are more or less throwing it away for no reason.