If you search with "스폰지밥 더빙" on YouTube or google, you'll see a few Korean-dubbed ones. You can do the same with 프렌즈 더빙 to find children's cartoons with "Friends" in the title, but I'm not sure if that's what you're looking for (If you're looking for Korean dubbing of Friends the American adult drama from the 90s, I doubt it exists). There aren't very many dubbed movies or series for adults, because dubbing is not popular these days. You can search for '더빙 외화' (dubbed foreign movies). There seem to be some old ones, like 초록 지붕 집의 앤 (Anne of Green Gables) and some episodes of older series.