Looking around online some people wonder where that moment comes from in an episode or a film but they don't know which one.
Even though I admit that I haven't seen every episode, film or TV Special, know enough to answer some of these. The first batch of question come from those who watch English dub compilations or common memes while the second is more general.
What's the episode with the bad Christopher Walken impression?
Extremely common especially for American fans since it was one of the few that was aired on Adult Swim. Lupin the Third Part 2: Episode 9 if you watch on streaming sites but Episode 10 in the proper order. Either Steal File M123 or Zenigatacon depending on translation.
For people not watching the English dub, it is due to George Marshall speaking in that way in that version. Oh and it is listed as that rather than Marcel Dulan due to Part 5. So if you can't find Marcel on here, that's why.
It is also the episode with the multiple Zenigatas, "Come on guys hustle up, we better get back there before my pants explode" and "Who wants Chicken Nuggets?". The latter was due to the English dub adding chicken jokes. Much of the dub compilations include moments from this one and the ones below.
What's the episode where Lupin says "Which weights more, a ton of trouble or a ton of dough?
Is the Leaning Tower of Pisa Standing? (English dub: Shaky Pisa) It's Episode 5 on streaming sites but 6 in the proper order.
As a note, this references the English dub. In the Japanese original, he says "which is heavier, a kilo of cotton or a kilo of a wad of bills?" Jigen responds with the second option in both.
For the English dub people, this is also the episode with "tectonic plates".
What's the episode where Goemon frees Lupin from the bear trap and throws it away?
I Can Hear Nessie's Song (English dub: 50 Ways to Leave Your 50-Foot Lover) Episode 3 on streaming sites but 4 in the proper order.
For the English dub fans, Goemon says "Ah, the old exploding bear trap in the ass trick." It is also the episode where Jigen goes on about "Big Bang Boomerang".
Outside of the dub, it is also the episode where Lupin is peddling for Fujiko and the animation mistake where Jigen's face is misplaced behind the animation cel of his neck.
What's the episode where Goemon says "Goemon Ishikawa is in the house!"?
The Great Thief Nezumi-Koozoo Makes His Appearance
The English dub compilations reference a fair bit from the episode as the dialogue was rewritten. The one moment that was kept similar was where "Rat Boy" (Nezumi-Kozo) talks about 007 but the English dub was referencing to Die Another Day and other Bonds.
What's the episode where Lupin and Jigen are floating in mid-air?
The Electroshock Pigeon Operation (English dub: Fry Me to the Moon)
What's the episode where Goemon is holding a turkey with the Zantetsuken?
Hitler's Legacy (English dub: To Be or Nazi Be)
What's the episode where Jigen drives and says "Oh yeah mama, work that chick for your daddy"?
I'll Tell You How to Transport Gold Bullion (English dub: Gold Smuggling 101)
Strangely enough, this is not quite an invention of the English dub even if it feels that way. The Japanese original says "There she goes, shaking her hips! She's a woman all right."
What's the episode where Jigen reads that magazine?
The PlayBohz magazine that had a man on the cover? Lupin the Third Part III: Episode 7. Garb, The Grim Reaper or The Man Called Death Gurve depending on your translation. The wiki page even has a screenshot for your convenience.
Where does the scene where Jigen and Goemon are dressed as women come from?
Operation: Return the Treasure. It is when they are stealing from the Moulin Rouge.
What's the episode with the giant Fujiko?
The Mysterious World of Madame X
What's the episode with the penguins?
Lupin's Big South Pole-North Pole Adventure
What's the episode where Lupin hangs around with a cocktail waitress?
The Name of the Cocktail Is Revenge
What's the episode where Zenigata manages to handcuff Lupin, Jigen and Goemon?
Find the Treasure of Lupin I however it is also a reference to the manga chapter Inspector Lupin (or the one before it).
What episode does Lupin take off his face mask of himself? (spoiler)
Viva Lupin III from Part 5 however it is an obscure manga reference. Lupin is also implied to wear a wig in the second opening of Part III and The Legend of The Gold of Babylon where he is shown to be bald.
What's the episode where Lupin is a weather vane/weather cock?
Lupin Vs. the Mystery Man with Two Faces. At one point it was even made as a figure that you could buy.
What episodes or films that feature Zenigata as a drag?
Quite a few, the most referenced one is Farewell to Nostradamus. Zenigata was also dressed up as a woman in Steal Everything of Lupin's and Poison, Magic and Lupin III. There is a picture of Zenigata dressed up as Fujiko but believe that comes from Mankatsu (not sure).