Steps:

1.Select the resource Gantt chart.
2.Click on the [Display Settings] button on the toolbar to display information about the display settings in the properties window.
3.Change the value of the property “Objects for which to show connection line” in the Bar tab to “Last selected object”.
4.By clicking on the bar for which you want to display a connection line, you can display a connection line. You can display a connection line for only one order at a time.
5.Clicking the mouse on other part of the chart than the bar will remove the connection line.