Prueba a cambiar el ? por @ en los parametros de tu consulta, de manera que te queda asi:
Código VB:
Ver originalPrivate Sub CargarData1()
Dim cad As String = "Database=Pacientes;Data Source=localhost;User Id=root;Password=utan"
Using cnn As New MySqlConnection(cad)
Dim query As String = "select * from pacientesdiagnosticos WHERE idpaciente = @id"
Dim cmd As New MySqlCommand(query, cnn)
cmd.Parameters.AddWithValue("@id", CInt(TextBox1.Text))
Dim da As New MySqlDataAdapter(cmd)
Dim dt As New DataTable
Try
Dim Cmd1 As New MySqlCommandBuilder(da)
da.Fill(dt)
Diagnosticos.DataSource = dt
Catch ex As MySqlException
MsgBox(ex.Message)
End Try
End Using
End Sub
Saludos