It's now available in the latest sandbox build (2019.4.4058):
https://javascript.daypilot.org/sandbox/
Example:
var col = dp.columns.find("2019-10-07"); // DayPilot.Column object
var events = col.events.all();
The DayPilot.Column object is also available in onBeforeHeaderRender and onHeaderClick as args.column.