Learn Hardcore Japanese: watasi ha sigoto no ato, ie de kigaemasu.

It marks the topic. 私 is being set up as “as for me,” and the rest of the sentence tells you something about that topic. Using が here would put focus on “I” as the subject (as opposed to someone else) and sounds odd unless you’re contrasting: 私が仕事のあと、家で着替えます (It’s I who change…).

Why is it 仕事のあと and not 仕事あと?

の links the noun 仕事 to the noun あと, literally “the after of work.” Without の, it’s ungrammatical in this structure. There is a compact written style 仕事後 (no の), but that’s more formal/newsheadliny. In everyday speech/writing, use 仕事のあと.

Can I say 仕事のあとに or 仕事のあとで? Are they different?

All three are acceptable:

仕事のあと、… (neutral, common)
仕事のあとで、… (very common in conversation; clearly “after that, …”)
仕事のあとに、… (more like “at the time after work,” a bit more written/point-in-time) Nuance differences are small; in most everyday contexts they’re interchangeable.

Why is there a comma after あと?

It just marks a natural pause after the time phrase and improves readability. You can omit it: 仕事のあと家で着替えます. Both are fine.

Why is it 家で and not 家に?

で marks the location where an action takes place. You change clothes at home, so 家で. Use 家に with existence or arrival: 家にいる (be at home), 家に帰る (go home).

How should I read 家 here—いえ or うち? Is there a nuance difference?

Both are possible.

いえ: the physical house/building.
うち: “my place/home,” more personal. In casual speech many people would say うちで着替えます. In writing, 家で can be read either way from context.

What exactly does 着替えます mean?

It means “(I) change clothes / get changed.” The subject “I” is understood from context. The verb is polite present form.

What’s the plain (dictionary) form and some basic conjugations of 着替えます?

Dictionary: 着替える (きがえる, ichidan/ru-verb)
Polite present: 着替えます
Polite past: 着替えました
Negative: 着替えない / 着替えません
Te-form: 着替えて
Volitional: 着替えよう / 着替えましょう
Potential: 着替えられる (can get changed)

Is 着替える transitive? Can I say 服を着替えます?

Traditionally, 着替える is intransitive (“to change clothes”), so you don’t need an object. To specify what you change into, use に: パジャマに着替える. Many natives do say 服を着替える, and major dictionaries now list it as acceptable colloquial usage, but some teachers/style guides still prefer avoiding it. Safest options:

着替える (no object)
パジャマに着替える (change into pajamas)
着替えをする (noun+する)

How do I say “change into pajamas” or “change out of my work clothes”?

Change into pajamas: パジャマに着替えます。
Change out of work clothes: 仕事着を脱いで、（私服に）着替えます。 or 仕事着から私服に着替えます。

Is the sentence talking about the present or the future?

The polite non-past 着替えます covers both habitual present and future. Without context, it usually reads as a routine: “After work, I (usually) change at home.” With a future context, it can mean “I will change at home after work.”

Can I drop 私? Do Japanese people usually say it?

Yes, you can drop it, and it’s natural: 仕事のあと、家で着替えます。 Subjects are often omitted when obvious from context. Keep 私 if you need contrast/emphasis or clarity.

Can I move the phrases around? What’s the preferred order?

Typical order is Time > Place > Verb:

仕事のあと、家で着替えます。 (most natural) Other orders are possible but can sound marked. For contrast you can say 家では着替えます (“at home, at least, I change”) using は on the place phrase.

How does 〜のあと compare with 〜てから and 〜たら?

仕事のあと（で）着替えます。 Neutral “after work, (I) change.”
仕事してから着替えます。 Emphasizes sequence “do X and then Y,” often implying Y happens soon after X.
仕事が終わったら着替えます。 “When/if work is finished, (I) change,” with a conditional nuance. All are common; choose based on the nuance you want.

Is there any difference between writing あと vs 後? What about 仕事後?

あと / 後: same word; using kana (あと) is very common in everyday writing. 後 is the kanji form.
仕事後: compact Sino-Japanese compound, feels formal/headline-like. In conversation, prefer 仕事のあと.

Does the で in あとで mean the same thing as the で in 家で?

No. In あとで, the で is part of the fixed time expression meaning “afterward.” In 家で, で is the location-of-action particle. Same spelling, different roles.

Could I say 会社のあと to mean “after work”?

Avoid 会社のあと; it literally means “after the company.” Use:

仕事のあと
勤務（きんむ）のあと (formal)
会社が終わったあと
勤務後 (formal/written)

How would I say “before work” instead?

Use 前(まえ):

仕事の前（に）、家で着替えます。 “Before work, I change at home.” As with あと, 前に is common; 前 without に also works in this kind of adverbial position.