DNS cache on macOS (Catalina)
It's very likely you don't actually have a DNS cache. If you do, dscacheutil -cachedump seems relevant here, probably sudo dscacheutil -cachedump. That said, I don't see any cache on any system I have, neither server-oriented systems nor end-user laptops.

See man dscacheutil for more.

Denis' answer via the comment will let you see lookups as they happen, but the DNS cache is very short lived if present at all.

Is there an actual problem at hand?