The set-up:
This demo shows how to get reference of the dataItem bound to the column where the custom command key is pressed, and shows the respective info in a Window. You can use the dataItem to update the Grid as well:
http://demos.telerik.com/kendo-ui/grid/custom-command
Here is an example as well:
http://dojo.telerik.com/abUHI Take a look at the showDetails function