Добавьте файлы проекта.

musicschoolapp/Pages/Instr.xaml

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+<Page x:Class="musicschoolapp.Pages.Instr"
+      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
+      xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
+      xmlns:local="clr-namespace:musicschoolapp.Pages"
+      mc:Ignorable="d" 
+      d:DesignHeight="450" d:DesignWidth="800"
+      Title="Instr">
+
+    <Grid>
+        <DataGrid x:Name="dGridStudent" AutoGenerateColumns="False" SelectionChanged="dGridStudent_SelectionChanged" MouseDoubleClick="dGridStudent_MouseDoubleClick">
+            <DataGrid.Columns>
+                <DataGridTextColumn Header="ID" Binding="{Binding Id_instrument}"></DataGridTextColumn>
+                <DataGridTextColumn Header="Название" Binding="{Binding Name_instrument}"></DataGridTextColumn>
+                <DataGridTextColumn Header="Дата приобретения" Binding="{Binding Date_receiving}"></DataGridTextColumn>
+                <DataGridCheckBoxColumn Header="Личный?" Binding="{Binding isPersonal}"></DataGridCheckBoxColumn>
+            </DataGrid.Columns>
+        </DataGrid>
+    </Grid>
+</Page>