[villagetinker]

OP, you should be able to carefully take a knife (or similar) and probe along the seam between the sink and the countertop. Epoxy will be very hard, and the knife will tend to slide, silicone will tend to be much softer, and the knife will tend to stick. You can also take a look from the cabinet to bottom of the countertop to confirm the wingnuts. If you are just replacing the sink, make sure the new one is the same size, the depth can be different, but this will impact the drain plumbing and the garbage disposal mount.