nitiyou ha daigaku ni ikanakute mo yoi node, ie de nihongo no syousetu wo yomimasu.

Both are correct.

• 日曜 is a shortened form of 日曜日
• 日曜は and 日曜日は both mean as for Sunday / on Sundays

The shorter form 日曜 is very common in everyday Japanese. A learner should just know that both versions are natural.

Also, は marks Sunday as the topic of the sentence:

• 日曜は = As for Sunday(s), ...

So the sentence is setting up Sunday as the time being talked about.

Here, は marks the topic, not simply the subject.

• 日曜は means As for Sunday or On Sundays
• It gives the sentence a frame: when it comes to Sunday, this is what happens

This often sounds more natural in Japanese than directly saying something like On Sunday with a simple time marker.

It can also imply a contrast, depending on context:

• 日曜は大学に行かなくてもよい
  = On Sundays, I don’t have to go to university
  This may suggest that on other days, I do.

に marks the destination of movement.

• 大学に行く = to go to university
• 家で読む = to read at home

So:

• 大学に = destination
• 家で = location where an action happens

This is a very common contrast:

• に with going / coming / returning
• で with doing an action at a place

This is a very important grammar pattern:

• 行く = to go
• 行かない = not go
• 行かなくて = a form based on the negative
• 行かなくてもよい = it is good even if you do not go
• natural English meaning: you do not have to go

So the pattern is:

• Verb nai-form + なくてもよい / いい
• meaning: don’t have to ...

Examples:

• 食べなくてもいい = you don’t have to eat
• 行かなくてもいい = you don’t have to go
• 勉強しなくてもいい = you don’t have to study

A key point: this does not mean must not go.

• 行かなくてもよい = don’t have to go
• 行ってはいけない = must not go

Those are very different.

よい and いい are basically the same word here.

• よい is a more formal or written-sounding form
• いい is more common in everyday conversation

So:

• 行かなくてもよい
• 行かなくてもいい

Both mean don’t have to go.

In textbook-style Japanese, official writing, or slightly more formal sentences, よい often appears.

ので gives a reason or cause:

• 大学に行かなくてもよいので、家で日本語の小説を読みます。
• Since I don’t have to go to university, I read a Japanese novel at home.

Both ので and から can mean because / since, but they feel a little different:

• ので sounds softer, more explanatory, and often a bit more polite
• から can sound more direct

So:

• 行かなくてもよいので = since I don’t have to go
• 行かなくてもよいから = also possible, but slightly more direct

In many learning materials, ので is introduced as a gentler way to give reasons.

Because the action reading happens at home.

• 家で読む = read at home
• 家に行く = go home

Use で for the place where an action takes place:

• 図書館で勉強する = study at the library
• 家で食べる = eat at home

Use に for destination or existence:

• 家に帰る = return home
• 家にいる = be at home

So in this sentence, the important action is 読みます, and reading happens at home, so で is correct.

Here, の connects two nouns.

• 日本語 = Japanese language
• 小説 = novel
• 日本語の小説 = a Japanese-language novel or a novel in Japanese

So の is linking the nouns, showing that the novel is related to Japanese.

This is different from saying:

• 日本の小説 = a Japanese novel, meaning a novel from Japan or by a Japanese author

That is an important difference:

• 日本語の小説 = a novel written in Japanese
• 日本の小説 = a Japanese novel in national/cultural origin

Japanese nouns usually do not mark singular or plural the way English does.

So 小説 could mean:

• a novel
• novels

The exact meaning depends on context.

In this sentence, English often uses a Japanese novel because it sounds natural if you are describing what you do. But depending on context, I read Japanese novels at home could also be possible.

Japanese often leaves number unspecified unless it really matters.

Japanese non-past forms cover several ideas that English separates.

• 読みます can mean:
  • read
  • will read
  • do read / usually read

In this sentence, the meaning depends on context:

• If the speaker is talking about a habit, it means I read
• If the speaker is talking about a plan for this coming Sunday, it can mean I will read

Japanese often uses the same form for present and future. Context tells you which is intended.

Japanese often leaves out the subject when it is clear from context.

So even though there is no explicit 私 in the sentence, the meaning can still be:

• I don’t have to go to university on Sundays, so I read a Japanese novel at home.

This omission is extremely common in Japanese. If the speaker is already understood, adding 私 may be unnecessary or even sound unnatural.

So the subject is not missing in the sense of being unclear to Japanese speakers; it is just omitted because context carries it.

By itself, 日曜は often sounds like on Sundays or as for Sundays, so it can easily suggest a habitual meaning.

Because the sentence also uses a non-past verb, the whole sentence can naturally be understood as a regular pattern:

• On Sundays, I don’t have to go to university, so I read Japanese novels at home.

However, in the right context, it could also refer to one specific Sunday. Japanese often relies on context rather than forcing the distinction every time.

If someone wanted to make this Sunday clearer, they might say:

• 今度の日曜日は = this coming Sunday
• 今週の日曜日は = this Sunday

So without extra context, 日曜は often feels more general or habitual.