Questions & Answers about Apenas él se quite el abrigo, va a ir a la ducha.
Why do we use the subjunctive quite after apenas here?
Because apenas (as soon as) introduces a time clause referring to a future, anticipated event. He hasn't taken off the coat yet! Whenever apenas, en cuanto, or tan pronto como point to a future action, you must follow them with the present subjunctive.
Can I use en cuanto or tan pronto como in this sentence instead?
Why does it use the reflexive se quite instead of just quite?
We use the reflexive verb quitarse when someone is taking off their own clothing. If you used the non-reflexive quitar, it would mean removing something in general, like taking a plate off the table.
Why does it say el abrigo (the coat) instead of su abrigo (his coat)?
In Spanish, it is standard to use definite articles like el or la instead of possessive adjectives like su for clothing and body parts. The reflexive pronoun se already makes it perfectly clear whose coat is being taken off.