Tā juéde zuò zhōngwén zuòyè bú tài jiǎndān.

觉得 means to feel or to think in the sense of giving a personal opinion.

In this sentence, 他觉得... means he thinks/feels that...

So the structure is:

• 他 = he
• 觉得 = thinks / feels
• 做中文作业不太简单 = doing Chinese homework is not very easy

A useful pattern is:

A 觉得 B = A thinks that B

做 means to do.

So:

• 作业 = homework
• 做作业 = to do homework

In this sentence, 做中文作业 means to do Chinese homework.

If you remove 做, the sentence changes slightly:

• 他觉得中文作业不太简单 = He thinks Chinese homework is not very easy.
• 他觉得做中文作业不太简单 = He thinks doing Chinese homework is not very easy.

The version with 做 focuses more on the activity of doing it.

中文作业 usually means Chinese homework, most often homework for Chinese class.

It can also sometimes mean homework written in Chinese, depending on context, but for most learners the most natural understanding is:

• 中文 = Chinese language
• 作业 = homework
• 中文作业 = Chinese homework / Chinese-language homework

In Mandarin, nouns often modify other nouns directly, so 中文 comes before 作业 to describe what kind of homework it is.

Yes, but it is a softer way to say it.

• 简单 = simple / easy
• 不太简单 literally = not too simple or not very simple

In natural English, this often means:

• not very easy
• kind of difficult
• not exactly simple

It is usually less direct than saying:

• 很难 = very hard
• 不简单 = not simple

So 不太简单 sounds a bit milder and more understated.

This is because of a common tone change rule.

Normally, 不 is fourth tone: bù.
But when it comes before another fourth-tone syllable, it changes to second tone: bú.

Here:

• 不 = fourth tone
• 太 = fourth tone

So:

• 不太 is pronounced bú tài

This is called tone sandhi.

Because in Mandarin, adjectives can act like verbs.

So:

• 简单 can mean to be simple
• 难 can mean to be difficult
• 高兴 can mean to be happy

That means you do not usually need 是 before an adjective.

So these are natural:

• 作业很简单 = The homework is easy.
• 作业不太简单 = The homework is not very easy.

Using 是 before 简单 here would sound unnatural.

Mandarin often puts a full clause after verbs like 觉得.

So the sentence is built like this:

• 他 = he
• 觉得 = thinks
• 做中文作业不太简单 = doing Chinese homework is not very easy

In other words, everything after 觉得 is what he thinks.

This is very common in Mandarin:

• 我觉得这个老师很好。 = I think this teacher is very good.
• 她觉得今天很冷。 = She thinks today is very cold.

So the word order is normal and natural.

简单 is understandable and grammatical here, but many native speakers might prefer 容易 when talking about how easy or hard an action is.

Compare:

• 做中文作业不太简单
• 做中文作业不太容易

Both work, but 不太容易 often sounds a bit more natural for tasks or actions.

A rough difference:

• 简单 = simple
• 容易 = easy

So:

• 这个问题很简单。 = This question is simple.
• 这个问题很容易回答。 = This question is easy to answer.

Your sentence is fine, but learners should know that 容易 is also very common in this kind of situation.

Yes, but the tone changes slightly.

Some common alternatives are:

• 觉得 = think / feel
• 认为 = believe / consider
• 感觉 = feel

Examples:

• 他觉得做中文作业不太简单。
  = He thinks doing Chinese homework is not very easy.
  This sounds natural and conversational.

• 他认为做中文作业不太简单。
  = He believes doing Chinese homework is not very easy.
  This sounds a bit more formal or deliberate.

• 他感觉做中文作业不太简单。
  = He feels doing Chinese homework is not very easy.
  This emphasizes personal feeling more.

For everyday speech, 觉得 is usually the safest choice.

In careful dictionary-style pinyin, it is written juéde.

In actual speech:

• 觉 is usually clearly pronounced jué
• 得 is often a light/neutral syllable, so it sounds more like juéde

So learners should usually say:

• juéde

rather than stressing the second syllable strongly.

This is very common in spoken Mandarin: some second syllables become lighter and less stressed.