Go to the website of the New Jersey Division of Consumer Affairs and choose the "Licensee Search" page in the drop-down menu under "Highlights" (see the References for a link to that page).
Choose the type of licensee in the drop-down menu at the top of that page. Depending on what construction work they do, companies and individual contractors will most likely be listed under Electrical Contractor, Home Improvement Contractors, or Master Plumber. You may need to search each category separately.
Fill in the name of the company or the individual and the city. You can use partial words or leave some lines blank. For example, to see a list of all the contractors in a particular city, leave the name of the contractor blank and fill in the city only.
Click on "Start Search" to bring up the results. The date on which the information was last revised shows at the top of the results page.