If I understand well, you want to add npc on a transport like a boat or zepp ?
If so you just have to go on it and do a .gps, look for the "TransMapID" and the other "TransOffsetX" "TransOffsetY" "TransOffsetZ" "TransOffsetO".
Usually I just spawn the needed npc randomly in the world and change their coordinates with a sql request.
REPLACE INTO `creature` (`guid`, `id`, `map`, `zoneId`, `areaId`, `spawnMask`, `phaseMask`, `modelid`, `equipment_id`, `position_x`, `position_y`, `position_z`, `orientation`, `spawntimesecs`, `spawndist`, `currentwaypoint`, `curhealth`, `curmana`, `MovementType`, `npcflag`, `unit_flags`, `dynamicflags`, `VerifiedBuild`) VALUES (currentguid, entryofthenpc, mapid, 0, 0, 1, 1, 0, 1, TransoffsetX, TransoffsetY, TransoffsetZ, TransoffsetO, 300, 0, 0, 247, 0, 0, 0, 0, 0, 0);
Hope it help.