I don't have the code, but this is what I would try:
first of all, you don't need to use editor to edit features, you can just use featureLayer.applyEdits() method.
1, use a draw tool to draw a polygon withing a polygon in your featureLayer
2, save the geometry of the polygon you just drawn to a variable for update later
3, use featureLayer.selectFeatures() method to select the polygon you want to clip out
4, update the geometry of the polygon. you can use geometry.addRing() method. (may need to arrange the new ring counter-clockwise in order to create a whole)
5, Now the polygon you want to clip out has a new geometry with a whole in it which is the polygon you drawn, you can just use
featureLayer.applyEdits(null, feature, null) to update the clipped out polygon.
check the API references for the corresponding objects and methods.