VB.net - LINQ - WebForm Display next ID then submit new data

I have been working on a click even for the submit button but I need to display the EmployeeID in a textbox first. 
Should I show the ID on pageload?
Trying to accomplish the following:
1. match the employee first and last name and (employee ID),
2. return a message to the page if the employee already exists,
3. I also want to display the next available employee ID in a textbox.
 
Protected Sub btnUpdate2_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnUpdate2.Click
        Using context As New personnelDataContext()
            Dim employees = From c In context.Employees _
                Where (c.lastName.Contains(txtLastName.Text.Trim()) AndAlso c.firstName.Contains(txtFirstName.Text.Trim())) _
    ...