what are all the episodes that conan was kidnapped in.

If I remember correctly there are quite a few cases where he has been kidnapped.

Episode 43: Conan Edogawa Kidnapping Case (Episode 44, if you're looking for the English dub version.)

Episode 321 & 322: The Kidnapper's Disappearing Getaway Car

Episode 547 & 548: Two Days with the Culprit

And, if anda want to count specials, there's The Disappearance of Conan Edogawa: The Worst Two Days in History.

another episode is 845-846 in new episodes the other ones are also correct as well that the sebelumnya person answered