The hierarchy expand/collapse column is generated automatically by the Grid, so it is not present in the columns
configuration array and does not have a declarative template.
In order to inject additional content in this column, you will need to use the Grid's dataBound
event and programmatic DOM manupulation. This is a little more complex than necessary for such a simple goal, so what I would do in your shoes, is to add one more adjacent column like this:
This is the column declaration:
"<button class='myCustomButton k-button k-button-icon k-bare'><span class='k-icon k-i-pencil'></span></button>"
This is the click handler, which is attached after Grid initialization:
grid = $(
EmployeeID = grid.dataItem(args.target.closest(
"Custom button clicked, EmployeeID: "