i was trying to populate datatag fields in the event bubble but could not find any answer so i came up with my own hope it helps some one in future this is done server side when you hover above an event in the schedular
Protected Sub EventBubble1_RenderContent(ByVal sender As Object, ByVal e As DayPilot.Web.Ui.Events.Bubble.RenderEventArgs) Handles EventBubble1.RenderContent
Dim re As RenderEventBubbleEventArgs = e
'gets the events for notes
Dim da As New Data.SqlClient.SqlDataAdapter("SELECT [notes] FROM [mytable] WHERE [ID] = '" & re.Value & "'", ConfigurationManager.ConnectionStrings("myconnectionstring").ConnectionString)
Dim dt As New DataTable()
da.Fill(dt)
re.InnerHTML = dt.Rows(0).Item(0)
End Sub