Question

what is the subject in the sentence "switch off the fan."

Answer 1

Hiii,
_______________________________________________________________
The subject in the sentence is Fan 
(because switch off is predicate which tells about the subject fan)
_______________________________________________________________
HOPE IT HELPS.

Answer 2

Here in the sentence "Switch off the fan", the object is the fan.

Object in a sentence is the one for which the verb is applicable.
Here in the given sentence, the verb "Switching off" is for the fan.