Where to find Callback URL

I am using webhook to create bot for page. I got everything but not getting where to get Callback URL

I think you're misunderstanding the concept of webhooks. The Callback URL is simply the location that you want Facebook to deliver messages to.

For example: if you are running a server at https://my_awesome_service.com and you want it to receive facebook updates, you would first create a route (let's say /v1/facebook_subscriptions) in your service. Once that's ready, you would insert https://my_awesome_service.com/v1/facebook_subscriptions into that Callback URL field. Facebook will then do a GET on that URL, which your server must reply to correctly. After that's done, Facebook will start sending you POST's, based on the subscription fields you set up.

There's a lot more information about this in the Facebook API Docs.