If you can suspend it in water in a graduated cylinder and measure its weight and volume, you can get its density (or specific gravity). That would make a good double check of your jeweler's measurement of metal type.

That's how we checked specific gravity of a sample in College chemistry lab. Tie a thread around the sample. Read the marking on the grad cylinder before and after suspending it in the water. Measure the weight of the sample dry on a balance. Density is dry sample weight divided by amount of water displaced in the cylinder.

If the sample is a regular size, you can calculate its volume; your sample token doesn't appear to lend itself to that kind of calculation so you'd have to do the "water displaced" test to get volume. Pure gold is about twice the density of brass (19,000 vs. 8,500 in kg/cubic meter). Of course, if its closer to 12 k gold, there won't be as much difference in the density .