i used dig (domain information groper) to find all the subdomain of a domain.
There some site that hosting website and they give out free subdomain.
I want to find those subdomain.

i used the dig and found

*.example.com and another like forums.example.com

i think *.example.com is what im looking but * can mean anything.
so how to look into the * and see all the list?

See if this helps:

Domain Information Groper ( DIG ) Basics Tutorial

the video are the method i used to find the data about
*.example.com

the site is a hosting site that give out free subdomain like
123.example.com
abc.example.com

* can be anything

How to use DNS to find all the subdomain it hosting or any another way

According to this:

example.com - Wikipedia, the free encyclopedia

* can be anything as you say. It is simply a "place mark" as an example.

If I read the wiki correctly there is no "real" domain here.

example.com, example.net, and example.org are second-level domain names reserved by the Internet Engineering Task Force through RFC 2606, Section 3, for use in documentation and examples. They are not available for registration.

By implementing the reservation, the Internet Assigned Numbers Authority (IANA) made available domains to use in manuals and sample software configurations. Thus, documentation writers can be sure to select a domain name without creating naming conflicts if end-users try to use the sample configurations or examples verbatim.

When an address such as "yourusername@example.com" is used to demonstrate the sign-up process on a website, it indicates to the user they should fill in an actual e-mail address at which they receive mail. "example.com" is used in a generic and vendor-neutral manner.

As of 2009, these domain names resolve (in IPv4) to 208.77.188.166 and are managed by ICANN.

If I am mistaking your question there are other DNS "lookup tools" listed in this Google:

dns lookup - Google Search

i only use example.com as an example, i dont want to said the real domain in a forum.

Oh. I see. You were using example as an example.

I will do some more searching and post back anything I find.

Sorry for misunderstanding.

Try this:

Domain - reports and all about ips, networks and dns

i think the site will only list the subdomain that put themself in the google index.
i use the mouse and hover over the link and got
Redirect Notice
the site must had use the code to serach in the google something like this

url:example.com
and then list all the subdomain.

Because i also have a account in the hosting site but i didnt put my subdomain in the google's index and it didnt show up on the list..

From the site i learned that the domain have a Wildcard-DNS. Any idea what it is?

Wildcard-DNS - Google Search