I live in an apartment with several fire sprinkler in the ceiling.
If the sprinkler goes off due to fire or malfunction, can I turn it
off after the fire is out? Is it the same valve near the water heater
or is there a different one?
Im more worry about water damage (to electronics and computers) than
fire
damage. Perhaps because Ive never had a fire before and this is the
first
time I moved to a place with fire sprinklers.
Alternately, is there a switch to cut off power to computers or other
devices when it senses water? This would reduce short-circuits caused
by water when the device is powered.

Doubt you can turn it off. If the sprinkler does go off, you have more
problems than losing a computer.

In most cases, the valves are locked in the open position. This is to
avoid people turning them off and rendering the sprinkler system useless
when needed. You can even be arrested in some jurisdictions.

The fire department or the building maintenance can turn them off.