indexLabelLineThickness: Number

Sets the thickness of line connecting indexLabel with its corresponding dataPoint. It is only applicable when indexLabelPlacement is set to “outside”.

var  chart =  new  CanvasJS.Chart("container",
{
 .
 .
 data: [{
   type: "doughnut",
   dataPoints: [      
     {y: 24, indexLabel: "apple",  indexLabelLineThickness: 4}
  ]
 
  }],
 .
 . 
});
chart.render();