whichever quadrant most of the structure is in is the one it generated in

You'd have to identify the start of the structure. Every structure has a structure start. A stronghold start is the spiral staircase leading into the 5-way room. Fortress starts are crossroads with the center at an (11, 11) chunk coordinate (but there can be multiple per Fortress AFAIK). Village starts are at one corner at the center of the village where the bell is. You can find where the start is using /locate or viewing these structures on a tool like Amidst or MineMap. The location found with /locate or MineMap/Amidst is the start of the structure (more specifically the start chunk, which is all that matters). Using this you can probably memorize some starts to structures. The region that the start is in is also the region that the structure spawns in.

Note: @ above. The quadrant that most of the structure is in is not necessarily the region the structure spawns in. In theory you could have a ++ region Fortress that spreads to the +- region, with most of the Fortress in the +- region (even though the Fortress is ++).