Hello Muhammad, 

I believe you discussed the same requirement with other developer here in this forum thread. 

https://ko.infragistics.com/community/forums/f/ignite-ui-for-angular/124333/request-for-dashed-line/544792#544792

 We still don’t have dashed line capability in the IgxDataChart and we do have feature idea listed here , please vote for it for future implementation . 

https://ko.infragistics.com/community/ideas/i/ignite-ui-for-angular/configurable-lines-in-line-chart-ie-dotted-dashed-instead-of-solid-line---angular.

Thank you.