<dataGrid:RadDataGrid x:Name="dataGrid" ...>
    <dataGrid:RadDataGrid.Columns>
        <dataGrid:DataGridTextColumn x:Name="productNameColumn" PropertyName="ProductName">
            <dataGrid:DataGridTextColumn.HeaderContentTemplate>
                <DataTemplate>
                    <Grid>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition/>
                            <ColumnDefinition/>
                        </Grid.ColumnDefinitions>

                        <Label Text="Name" TextColor="Black"/>

                        <Label FontFamily="MyCustomFont.ttf#MyCustomFont"
                                    Text="&#xE717;"
                                    TextColor="Orange" HorizontalOptions="End" HorizontalTextAlignment="End" Grid.Column="1">
                            <Label.GestureRecognizers>
                                <TapGestureRecognizer Tapped="TapGestureRecognizer_Tapped"/>
                            </Label.GestureRecognizers>
                        </Label>
                    </Grid>
                </DataTemplate>
            </dataGrid:DataGridTextColumn.HeaderContentTemplate>
            <dataGrid:DataGridTextColumn.HeaderStyle>
                <dataGrid:DataGridColumnHeaderStyle OptionsButtonFontSize="0" FilterIndicatorFontSize="0"/>
            </dataGrid:DataGridTextColumn.HeaderStyle>
        </dataGrid:DataGridTextColumn>
    </dataGrid:RadDataGrid.Columns>
</dataGrid:RadDataGrid>

public partial class YourPage : ContentPage
{
    private readonly MethodInfo generateOptionsTapContextMethodInfo;

    public YourPage()
    {
        InitializeComponent();

        this.generateOptionsTapContextMethodInfo = this.dataGrid.GetType().GetMethod(
            "GenerateFilteringCommandContext", 
            BindingFlags.NonPublic | BindingFlags.Instance);
    }

    private void TapGestureRecognizer_Tapped(object sender, EventArgs e)
    {
        if (this.generateOptionsTapContextMethodInfo != null)
        {
            // Get a reference to the column, this is needed to invoke a command
            var context = this.generateOptionsTapContextMethodInfo.Invoke(
                this.dataGrid, 
                new object[] { this.productNameColumn });

            // Invoke the command service that opens the options button
            this.dataGrid.CommandService.ExecuteDefaultCommand(
                Telerik.XamarinForms.DataGrid.Commands.DataGridCommandId.OptionsTap, 
                context);
        }
    }
}