paper.localToClientPoint(p)

Transform the point p defined in the local coordinate system to the client coordinate system.

var rightMidPoint = element.getBBox().rightMiddle();
var clientPoint1 = paper.localToClientPoint(rightMidPoint);
 // alternative method signature
var clientPoint2 = paper.localToClientPoint(rightMidPoint.x, rightMidPoint.y);
// Draw an HTML rectangle next to the element.
var div = document.createElement('div');
div.style.position = 'fixed';
div.style.background = 'red';
div.style.left = clientPoint1.x + 'px';
div.style.top = clientPoint1.y + 'px';
div.style.width = '40px';
div.style.height = '40px';
div.style.marginLeft = '10px';
div.style.marginTop = '-20px';
document.body.appendChild(div);