Hi miglage,

Thank you for posting in the community.

In this scenario you can use the ColumnFilterAdded client-side event in order to access the key of the column on which a filter has been added:

function WebDataGrid1_Filtering_ColumnFilterAdded(sender, eventArgs)
{
    var key = eventArgs.get_columnFilter().get_columnKey();
}

Please feel free to contact me if you have any questions.