Currently, chartkick is unable to accept functions because of the way it uses json for its parameters. I found this github discussion which discusses this. They mention a possible solution is to pass the function in as a string and then to modify how the json is deparsed similarly to this article.
Another possible solution, as I am under the impression that chartkick uses highcharts for its js, is to update the events after the page/chart has already loaded. I believe it would look something like this
$("#container").highcharts().series[0].update({
events:{
click: function (event, i) {
alert(event.point.name);
}
}
})