public Chart3DHitInfo CalcHitInfo(
    Point point
)

Public Function CalcHitInfo(
    point As Point
) As Chart3DHitInfo

<dxc:Chart3DControl x:Name="chart" MouseUp="Chart3DControl_MouseUp">
    ...
    <dxc:Series3DStorage>
        <dxc:Series3D DisplayName="Function">
            ...
            <dxc:Series3D.View>
                <dxc:SurfaceSeriesView MarkerVisible="True">
                    ...
                </dxc:SurfaceSeriesView>
            </dxc:Series3D.View>
        </dxc:Series3D>
    </dxc:Series3DStorage>
</dxc:Chart3DControl>

using DevExpress.Xpf.Charts;
using System.Windows;
//...
private void Chart3DControl_MouseUp(object sender, System.Windows.Input.MouseButtonEventArgs e) {
    Chart3DHitInfo hitInfo = chart.CalcHitInfo(e.GetPosition(this));
    if (hitInfo.InSeries) {
        string str;
        if (hitInfo.SeriesPoint != null) {
            SeriesPoint3D point = hitInfo.SeriesPoint;
            str = $"X: {point.NumericXArgument:f2}, Y: {point.NumericYArgument:f2}, Z: {point.Value:f2}";
            MessageBox.Show(str);
        }
        if (hitInfo.AdditionalItem != null) {
            SurfacePoint surfacePoint = (SurfacePoint)hitInfo.AdditionalItem;
            str = $"X: {surfacePoint.X:f2}, Y: {surfacePoint.Y:f2}, Z: {surfacePoint.Z:f2}";
            MessageBox.Show(str);
        }
    }
}

Imports DevExpress.Xpf.Charts
Imports System.Windows
'...
Private Sub Chart3DControl_MouseUp(ByVal sender As Object, ByVal e As System.Windows.Input.MouseButtonEventArgs)
    Dim hitInfo As Chart3DHitInfo = chart.CalcHitInfo(e.GetPosition(Me))
    If hitInfo.InSeries Then
        Dim str As String
        If hitInfo.SeriesPoint IsNot Nothing Then
            Dim point As SeriesPoint3D = hitInfo.SeriesPoint
            str = $"X: {point.NumericXArgument:f2}, Y: {point.NumericYArgument:f2}, Z: {point.Value:f2}"
            MessageBox.Show(str)
        End If
        If hitInfo.AdditionalItem IsNot Nothing Then
            Dim surfacePoint As SurfacePoint = CType(hitInfo.AdditionalItem, SurfacePoint)
            str = $"X: {surfacePoint.X:f2}, Y: {surfacePoint.Y:f2}, Z: {surfacePoint.Z:f2}"
            MessageBox.Show(str)
        End If
    End If
End Sub