shu: I'm not sure where the confusion stemmed from by as littledan said, just creating an error inside the shadow realm and observing its stack there is the issue. Here is a potential example:

const child = new ShadowRealm();
child.evaluate(`
const originalPrepare = Error.prepareStackTrace;
Error.prepareStackTrace = function(error, structuredStackTrace) {
  for (const callSite of structuredStackTrace) {
    console.log(callSite.getFunctionName(), callSite.getFunction());
  }
  return originalPrepare(error, structuredStackTrace);
});
`);
const getStack = child.evaluate(`function() {
  try { null.error } catch (e) { return e.stack; }
}`);
console.log(getStack());