Getting and changing the position of a g
element is relatively straightforward. For example like this:
var g = d3.select("#myG");
// get x position
var currentx = d3.transform(g.attr("transform")).translate[0];
// set x position
g.attr("transform", "translate(" + (currentx + 100) + ",0)");
Edit:
If you have a raw DOM element, select it with D3 first:
var currentx = d3.transform(d3.select(this).attr("transform")).translate[0];