Legal Question in Intellectual Property in Illinois

You would consult an intellectual property or copyright attorney. That is work that I concentrate in.

You have not specified what you mean by "use other's work". If the "work" you are referring to is a work of authorship, such as a movie, book, music, picture, and so on, then you need a copyright lawyer. The next question would be how you want to use the work. There are a lot of uses of copyrighted works that are not within the scope of the copyright, but other specific, and limited uses are.

If you mean "work" in the sense of a patented invention, then you would be looking for a patent lawyer.

If you are referring to a trademarked product, then you will want an attorney versed in trademark law.

Finally, if the "work" is none of the above, but is in the category of "trade secrets," you would want to consult an attorney familiar with trade secret law in your state. (For copyrights, trademarks and patents, federal law applies, and an attorney in any state may be able to assist you.)