@mhdajmalik,

You can set indexLabelLineThickness to show lines drawn from dataPoint to the indexLabel, which defaults to 0 in every chart-type except pie/doughnut. Please take a look at this jsfiddle.

If you specifically looking to show lines downwards, you can do so with couple of lines of code. Please take a look at this jsfiddle.

—
Vishwas R
Team CanvasJS