See Tracker Examples
<oxy:Plot.DefaultTrackerTemplate>
<ControlTemplate>
<oxy:TrackerControl Position="{Binding Position}" BorderThickness="2" BorderBrush="LightSteelBlue" LineStroke="SteelBlue" LineExtents="{Binding PlotModel.PlotArea}">
<oxy:TrackerControl.Background>
<LinearGradientBrush EndPoint="0,1">
<GradientStop Color="#B0C4DE" />
<GradientStop Offset="1" Color="#f0ffffff" />
</LinearGradientBrush>
</oxy:TrackerControl.Background>
<oxy:TrackerControl.Content>
<UniformGrid Columns="2" Canvas.Left="{Binding Position.X}" Canvas.Top="{Binding Position.Y}" Margin="6">
<TextBlock Text="{Binding Series.Title}" FontWeight="Bold" FontSize="15" Foreground="Black" />
<TextBlock Text="{Binding Series.Tag}" Foreground="Black"/>
<TextBlock>
<Run Text="X:" FontWeight="Bold" Foreground="Black" />
<Run Text="{Binding DataPoint.X, StringFormat='{}{0:0.000}'}" Foreground="Black"/>
</TextBlock>
<TextBlock>
<Run Text="Y:" FontWeight="Bold" Foreground="Black" />
<Run Text="{Binding DataPoint.Y, StringFormat='{}{0:0.000}'}" Foreground="Black" />
</TextBlock>
</UniformGrid>
</oxy:TrackerControl.Content>
</oxy:TrackerControl>
</ControlTemplate>
</oxy:Plot.DefaultTrackerTemplate>
Good luck