I am not sure you will find a marking on the gypsy that indicates what chain should be used, but for boats your size the most common gypsy uses 5/16" G4 hi-tensile chain. The chain is marked with "G4" on the outside edge in the middle of the links. If you don't have G4, I'm not sure how the other flavors of chain are marked if at all.
The manual for the windlass should list the possible gypsies that are available. The most common is 5/16" and the next most common is 3/8".
If the chain on the anchor is just a length attached to a line, that chain may not be G4. If the anchor rode is all chain, the original buyer should have matched the chain to the gypsy.