This is around the overflow drain, directly across from the spigot.
It's had its day. Time to replace.
Meanwhile, why is your drain pipe up so high? It looks as though it's not fitted properly and there is no room for a strainer, etc.
You really cannot. You need to replace it. If money is tight try Habitat for Humanity. Home Depot has sales on these sinks all the time.
Robyn, thank you. Now just to find the right color--the sink is 30 years old. This is a bathroom sink, not a kitchen sink and the overflow drain is in the typical place.
I would contact Kohler and send them photos of the sink - they have good customer service and maybe they will repair or replace it depending on the age
Thanks all. I ordered ice grey Porc-a-Fix and since the sink is Kohler's ice grey color, I hope that will do the trick.