What is the best material to use to repair this
I can’t tell from the photo, is just the paint chipping or did the epoxy / glass fracture as well? If the epoxy/glass is fractured and water can penetrate, you’ll have to do a proper epoxy/glass repair. If it’s just the paint that’s chipped (real common with NSP’s) all you need to do is to prep and repaint the area. The “proper” way would be to sand the paint edges smooth, give it a couple coats of poly-urethane primer, sand again, and then finish with a couple coats of matching poly-urethane paint. Then polish to blend in the paint edges. If you want a quick and dirty fix, I’ve used “Epoxy appliance repair paint” with good success. Comes in little 0.5 oz bottles with a built in brush. The color matches fairly closely and dries in 15 minutes.