Try using this code:

 <ig:XamTimeline x:Name="Timeline">
            <ig:XamTimeline.Axis>
                <ig:DateTimeAxis SelectedTimeChanged="DateTimeAxis_SelectedTimeChanged" />
            </ig:XamTimeline.Axis>

...

private void DateTimeAxis_SelectedTimeChanged(object sender, DateTimeChangedEventArgs e)
{
     IList<EventEntry> entries = this.Timeline.GetEntries(e.NewTime);
}