Tôi nghĩ rằng công việc này khá tốt.

Rằng introduces the clause that follows nghĩ and works a bit like that in English:

• Tôi nghĩ rằng công việc này khá tốt.
• I think that this job is quite good.

In Vietnamese, rằng is more formal or explicit. It helps mark clearly that what follows is the content of the thought.

Yes. Very often, especially in everyday speech, rằng is omitted:

• Tôi nghĩ công việc này khá tốt.

This is completely natural and very common.
Using rằng sounds a little more formal, careful, or written.

In Vietnamese, demonstratives like này usually come after the noun.

So:

• công việc này = this job / this work
• literally: job this

This is normal Vietnamese word order. English says this job, but Vietnamese says job this.

Công việc can mean:

• job
• work
• task, depending on context

In this sentence, it most naturally means this job or this piece of work. Vietnamese often relies on context more than English does, so the exact translation can vary.

Khá means something like:

• quite
• fairly
• rather

So khá tốt means quite good or fairly good.

It is milder than:

• rất tốt = very good

So the speaker is giving a positive opinion, but not the strongest possible one.

Tốt is a very common adjective meaning good. It can describe many things:

• công việc tốt = good job/work
• người tốt = good person
• sức khỏe tốt = good health

In this sentence, tốt describes the quality of công việc này.

The structure is:

• Tôi = subject
• nghĩ = verb
• rằng công việc này khá tốt = content of the thought

So the pattern is basically:

Subject + think + that-clause

More literally:

• Tôi = I
• nghĩ = think
• rằng = that
• công việc này = this job/work
• khá tốt = quite good

Yes. Vietnamese pronouns change depending on relationship, age, and tone.

For example:

• Tôi nghĩ rằng công việc này khá tốt. → neutral, polite
• Mình nghĩ rằng công việc này khá tốt. → more casual, friendly
• Em nghĩ rằng công việc này khá tốt. → used if the speaker is younger/lower in status relative to the listener

So tôi is not the only way to say I, but it is a safe and common one for learners.

Yes, but in conversation people would very often say:

• Tôi nghĩ công việc này khá tốt.

This sounds a little more natural in everyday speech because rằng is often dropped.
The full version with rằng is still correct and natural, just slightly more formal.

Yes. Khá tốt often sounds a bit measured or moderate.

Depending on context, it may suggest:

• fairly good
• pretty good
• decent

So if someone says Tôi nghĩ rằng công việc này khá tốt, it is positive, but it may sound a little less strong than a full enthusiastic endorsement like:

• Tôi nghĩ rằng công việc này rất tốt. = I think this job is very good.

A rough guide:

• Tôi: mid-falling in Southern speech, level-ish in Northern citation style depending on analysis; pronounced roughly like toy but with Vietnamese vowel quality
• nghĩ: has the ngã tone in standard Northern Vietnamese
• rằng: low/heavy tone
• công việc: công and việc each have their own tones; việc has a checked/heavy tone
• này: rising tone
• khá: rising tone
• tốt: checked/heavy tone

For a learner, the most important thing is to learn each word together with its tone, not just the consonants and vowels. Vietnamese tones are essential for being understood.

You can, but it will sound unnatural if you keep Vietnamese word order too closely.

A word-by-word gloss is:

• Tôi = I
• nghĩ = think
• rằng = that
• công việc này = job/work this
• khá tốt = quite good

Natural English would be:

• I think that this job is quite good.
• or simply I think this job is quite good.

So a literal gloss is useful for learning structure, but not always for producing natural English.