hii,

here your py updated code 
from odoo import models, fields, api

from odoo.exceptions import ValidationError

import re

class HrEmployee(models.Model):

    _inherit = 'hr.employee'

    work_email = fields.Char(string="Work Email")

    @api.onchange('work_email')

    def _onchange_work_email(self):

        if self.work_email:

            email = self.work_email.strip()

            pattern = r'^.+@([a-zA-Z0-9\-]+\.)+[a-zA-Z]{2,}$'

            if not re.match(pattern, email):

                raise ValidationError("Please enter a valid email address.")

XML (View) – Do NOT add on_change in XML

Just define the field like normal:

<field name="work_email"/>

Odoo will trigger the @api.onchange automatically when the field changes in the UI.

i hope it is use full