Works with enemy opening door:
ctf_2fort both blu spawn doors
ctf_2fort left red spawn door
ctf_well both red & blu right spawn doors
cp_coldfront second point both red & blu spawn doors
cp_foundry second point both red & blu spawn doors
cp_dustbowl first stage blu right spawn door
cp_dustbowl first stage blu middle spawn door (needs to be in the precise spot to work)
cp_dustbowl first stage red spawn and second stage blu spawn doors
cp_dustbowl second stage red spawn and third stage blu spawn doors (good for getting rid of teles and evacuating)
cp_dustbowl third stage red spawn doors except first point door
cp_gravelpit right red spawn door (unsure about left)
cp_steel red spawn door by A
pl_badwater all red spawns
pl_badwater blu’s second spawn

Works with door unopened (you can use these any time to avoid enemy fire and teleport back to base when spawn-camping):
cp_5gorge both red & blu second point spawns (good for when camping as pyro)
cp_5gorge both red & blu far right first point spawn doors
cp_5gorge both red & blu far left first point spawn doors
cp_freight both red & blu right first spawn doors
cp_freight both red & blu middle point spawns
cp_degrootkeep front blu spawn
cp_dustbowl first stage left door spawn
cp_yukon all spawn doors except both red & blu second point spawns
cp_mountainlab both bottom red spawn doors
cp_steel spawn door close to area D (has a D sticker on the right side of it)
pl_badwater all blu spawns at first except middle door
pl_barnblitz blu last spawn balcony (useful for spawn campers evacuating)
pl_barnblitz red last lower right spawn
pl_frontier last red spawn:covers a huge area of balcony
pl_upward last red spawn door (good for using after second point is captured)
koth_lakeside

Does not work:
ctf_2fort red spawn door
ctf_doublecross
ctf_turbine
ctf_sawmill
ctf_well both red & blu left spawn doors
cp_5gorge cp_gorge middle first point both red & blu spawn doors
cp_gorge red spawn doors
koth_harvest
koth_nucleus
cp_gravelpit blu spawn (respawn area is limited to only the house that blu spawns in)
cp_junction (all respawn areas are small even for tf2 standards)
cp_mountainlab all other doors
cp_steel blu spawn
plr_hightower (due to small respawn areas in both spawns)
sd_doomsday (due to small respawn areas in both spawns)

Not tried:
ctf_2fort red blu intelligence spawns (haven’t tried open)
cp_badlands (haven’t tried open)
cp_coldfront (with doors open)
cp_fastlane (with doors open)
cp_freight  (haven’t tried open)
cp_granary (not tried open)
cp_gullywash (with doors open)
cp_process (haven’t tried open)
cp_snakewater (with all open)
cp_well (haven’t tried open)
cp_standin (haven’t tried red side)
cp_egypt all doors
cp_steel all spawn doors open
pl_frontier_final (with all open)
pl_upward (with doors open)

Not tested:
tc_hydro
cp_sawmill
cp_manor_event (probably the same as mountain lab)
pl_goldrush
pl_hoodoo (some respawn areas are too small, but i think red’s spawn in the second stage works)
pl_thundermountain
plr_hightower_event
plr_nightfall
plr_pipeline (some areas work with enemy opening door)
koth_badlands
koth_viaduct_event
koth_lakeside_event
koth_king
koth_viaduct
rd_asteroid
pl_cactuscanyon

Other tips:
Use the loadout script to quickly change respawn areas in case you need to spawn in another area (useful when at badwater’s red spawn to change between areas to get to your sentry faster as Engineer)
Useful for refilling metal for building sentry close to a spawn door than running back to a resupply closet (can also send you way back further away depending on map)
Useful for making quick trips to respawn lockers in case your health is low and on fire (depends on a maps forgivable respawn area boundry)