markerSize: Number

Sets the Size of the marker that is drawn. To display marker in area Chart, set markerSize to a value greater than zero. For line, scatter chart, size it is automatically set unless overridden.

• In line Charts, Markers are automatically disabled when there are large number of dataPoints. You can override this behaviour by manually setting markerSize to a value greater than zero.
• You can also set this property at dataPoint level- to highlight that dataPoint.

var  chart =  new  CanvasJS.Chart("container",
{
 .
 .
 data:[{
   markerSize: 10,

  },
 ]
 .
 .
});
chart.render();