I want to use clientside event to validate input textbox data from database ?

How do you have DevExpress if you're a beginner ? Doesn't that cost money ? To do it like this, you need an UpdatePanel from the ASP.NET AJAX toolkit to wrap it all up for you. IMO, your skillset will thank you if you avoid that nastiness and learn jQuery and use that to handle your AJAX call and setting your label values.

I am not surprised. But, no-one is going to write all the code for you. I've told you what bits you need, but even if I wanted to write it all, I couldn't based on what you've said. If you don't know how to do it, I've given you the keywords to google for articles and tutorials. If you're not able to or don't want to spend the time learning it, then you're not an appropriate person to be given this task, and it makes no sense for me to give you a free ticket this time, when all you'll be able to do with your next task, is to ask us to do your work again. You should do some learning, talk to your manager if need be, and post here when you've spent some time learning and writing code and have a specific question.