Learn/AddReg.xaml

<Window x:Class="LearnSchool.AddReg"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:extensions="using:Microsoft.Toolkit.Uwp.UI.Extensions"
        xmlns:ui="using:Microsoft.Toolkit.Uwp.UI"
        xmlns:local="clr-namespace:LearnSchool"
        mc:Ignorable="d"
        Title="AddReg" Height="450" Width="800">
    <Grid>
        <StackPanel Width="200" HorizontalAlignment="Center" VerticalAlignment="Center">
            <TextBlock HorizontalAlignment="Center">Название услуги</TextBlock>
            <TextBlock Name="ServName"/>
            <TextBlock HorizontalAlignment="Center">Длительность в минутах</TextBlock>
            <TextBlock Name="Duration"/>
            <TextBlock HorizontalAlignment="Center">Клиент</TextBlock>
            <ComboBox Name="Client"/>
            <TextBlock HorizontalAlignment="Center">Дата</TextBlock>
            <DatePicker Name="DateServ"/>
            <TextBlock HorizontalAlignment="Center">Время</TextBlock>
            <TextBox Name="TimeServ"/>
            <Button Click="MakeReg" Margin="0,10,0,0">Сделать запись</Button>
        </StackPanel>

    </Grid>
</Window>