Use SqlDataReader.

Refer below article.

Difference between DataReader, DataSet, DataAdapter and DataTable in C# and VB.Net

You need to check with HasRows property which makes sure query returns one or more rows.

Public Sub Insertcheck()
    Dim constring As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
    Using con As New SqlConnection(constring)
        Using cmd As New SqlCommand("SELECT bookedinv FROM maxbooked", con)
            cmd.CommandType = CommandType.Text
            con.Open()
            Dim dr As SqlDataReader = cmd.ExecuteReader()
            If dr.HasRows Then
                While dr.Read()
                    Dim name As String = dr("bookedinv").ToString()
                End While
            End If
            con.Close()
        End Using
    End Using
End Sub