hew to identify user on online shopping without login in asp.net

You can do the following:

When an unauthenticated user adds the first item to his cart, assign it an unique id.
Store that id in a cookie
Save in your database the change made to the cart, using that id as a primary key.
When the session times out:

Read from the cookie the value previously assigned to the user's cart
Restore the cart for the current session from the data stored in the database.
There is a downside:

Suppose you have stored an user's cart in a db, and the user never comes back. In this case you'll want to implement a cleanup policy, say, cart are stored for two weeks max.
This can happen also when the user clean his browser's cache
Take into account that a user can browse your site with different browsers (and thus, different caches/cookies)