Minecraft wiki entry for Trapdoor, associated text: Oak trapdoors generate as in villages, igloos, and shipwrecks.
Spruce trapdoors generate in taiga villages and shipwrecks.
Birch trapdoors generate in shipwrecks.
Jungle trapdoors generate in desert villages (around composters) and shipwrecks.
Dark oak trapdoors generate in shipwrecks.
Acacia trapdoors generate in shipwrecks in Bedrock Edition.
Iron trapdoors generate in ancient cities.‌[upcoming: JE 1.19]