On the following Dojo example
you will find a modified version of your code which now correctly displays the tooltips.
You will notice that I have moved the ToolTip initialization out of the dataBound event of the Grid. In addition to this, I have also changed the class target for the edit button to .k-grid-edit, so that the button can be targeted correctly.
Also, you can review the following how-to example
, which demonstrates how to show unique tooltips for every column row.