I am not your attorney and the information I am providing is educational only. You need to speak to a lawyer in your state about this promptly.
If it's not on the table it probably is not subject to patent protection. Find out the company's name and check its website out for any patent claims. Then trace back if there are any.
Unless the table has some very unique functional aspects it is unlikely that the current manufacturer has a desgin patent on the table. Seeing the table is key to any worthwhile analysis.
I doubt that they even have a registered copyright on the design unless again it is a unique design.
If you copy the design of the table in making your own you will be infringing their copyright in the design; and you could get sued. You can tweak the design but again you have to make sure that your design is not derivative of theirs. You need to consult with a copyright lawyer.
The table may have different patents protecting different aspects of the table. For example, the design of the table may be protected with a design patent and if there is some feature that gives the table some unique utility then the table may be protected with a utility patent. Either case, the best way to determine if a patent has been issued is to search through the US Patent and Trademark Office patent database which can be found at http://patft.uspto.gov/ If the table is a product of a major manufacturer, chances are any patents on the table will have been assigned from the inventor to the corporation. Therefore, one place to start is to search for all patents issued to the manufacturer. To do so, you would select an advanced search. Then select "assignee name" and enter the name of the manufacturer. You could also try searching for specific keywords that distinguish the table from other tables. For example, "revolving table", "extendable table", etc. For the most part you are fishing. However, law firms and patent search firms do provide a patent search service to perform the search for you. These searches identify the closest patent matches. One such firm providing patent search services is www.lapatentgroup.com