@meenasiva,
Indexlabels are rendered on top of stripline by default. However, when showOnTop property of stripline is set to true, stripline gets rendered on top of every other element including indexlabel. In order to view the indexlabel clearly in your scenario, you can set the indexLabelBackgroundColor to the chart background color. Please take a look at this JSFiddle for an example on the same.
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Manoj Mohan
Team CanvasJS