It is called a conductive ink pen. Here's a link to a kit. You would need to buy the little lights too in order to use lights with it.
Circuit Scribe Basic Kit – Includes Conductive Silver Ink Pen, and Everything You Need to Learn, Explore, and Create Your Own Circuits and Switches! https://www.amazon.com/dp/B00M2AV2G2/ref=cm_sw_r_cp_apa_2jPHBbMGTDD1B
Circuit Scribe Basic Kit – Includes Conductive Silver Ink Pen, and Everything You Need to Learn, Explore, and Create Your Own Circuits and Switches! https://www.amazon.com/dp/B00M2AV2G2/ref=cm_sw_r_cp_apa_2jPHBbMGTDD1B