wǒ bù dài yǎnjìng jiù kànbuqīngchu hēibǎn shàng de hànzì.

Here 就 links the two parts of the sentence and shows a direct result:

• 我不戴眼镜 = if I don’t wear glasses
• 就看不清楚黑板上的汉字 = then I can’t see the Chinese characters on the blackboard clearly

So 就 often means something like then, in that case, or as a result.

A very common pattern is:

• 不/没……就……
• 如果……就…… = if … then …

In this sentence, 如果 is omitted because it is understood from context. So the whole sentence feels very natural and compact.

戴 is the verb used for things you wear on your body, especially things you put on your head, face, hands, or accessories such as:

• 戴眼镜 = wear glasses
• 戴帽子 = wear a hat
• 戴口罩 = wear a mask
• 戴手表 = wear a watch

It is not the same as all English uses of wear. In Chinese, different kinds of clothing and accessories often use different verbs:

• 穿衣服 / 穿鞋 = wear clothes / shoes
• 戴眼镜 / 戴帽子 = wear glasses / a hat

So 戴眼镜 is the natural expression for wear glasses.

This is a very important Chinese pattern: the potential complement.

• 看清楚 = see clearly
• 看不清楚 = cannot see clearly

The structure is:

• verb + 得 + complement = able to do something in that way
• verb + 不 + complement = not able to do something in that way

So:

• 看得清楚 = can see clearly
• 看不清楚 = can’t see clearly

Here 不 does not simply negate 看 by itself. Instead, it shows inability to achieve the result 清楚.

They are similar, but not identical:

• 看不清楚 = cannot see clearly
  You can see something, but it is blurry or not distinct.

• 看不到 = cannot see it at all
  It is out of sight, blocked, too far away, etc.

So in this sentence, 看不清楚黑板上的汉字 suggests that the speaker can probably see the blackboard, but the characters are not clear enough to read.

In 黑板上的汉字:

• 黑板 = blackboard
• 上 = on / on the surface of
• 的 = links the location phrase to the noun
• 汉字 = Chinese characters

So literally it means:

• the Chinese characters that are on the blackboard

Here 上 does not mean only above. With objects like tables, walls, blackboards, paper, and screens, 上 often means on the surface of.

Examples:

• 桌子上的书 = the book(s) on the table
• 墙上的画 = the painting on the wall
• 黑板上的字 = the writing on the blackboard

的 is used to connect a descriptive phrase to a noun.

Here the phrase 黑板上 describes 汉字, so you need 的:

• 黑板上的汉字 = the Chinese characters on the blackboard

Without 的, the phrase would sound incomplete or ungrammatical in standard Mandarin.

A useful way to think of it is:

• [describing phrase] + 的 + noun

Examples:

• 桌子上的杯子 = the cup on the table
• 学校里的学生 = the students in the school
• 我喜欢的书 = the book(s) I like

Both are possible, but they are slightly different:

• 汉字 = Chinese characters
• 字 = characters / writing / words, depending on context

Using 汉字 is more specific. It emphasizes that the speaker cannot clearly see the Chinese characters on the blackboard.

In everyday speech, many people would also say:

• 我不戴眼镜就看不清楚黑板上的字。

That sounds very natural too. 字 is shorter and more casual, while 汉字 is a bit more explicit.

Both can appear in Chinese, but they mean slightly different things.

• 不戴眼镜 = don’t wear glasses / if I don’t wear glasses
  This often sounds general, habitual, or conditional.

• 没戴眼镜 = didn’t wear / am not wearing glasses
  This often refers to a specific situation or completed fact.

In this sentence, 不戴眼镜 works well because it expresses a general condition:

• If I don’t wear glasses, I can’t see the Chinese characters on the blackboard clearly.

If you say:

• 我没戴眼镜，就看不清楚黑板上的汉字。

that sounds more like a specific situation:

• I’m not wearing my glasses, so I can’t see the Chinese characters on the blackboard clearly.

Chinese often omits 如果 when the meaning is already clear from context.

So both of these work:

• 如果我不戴眼镜，就看不清楚黑板上的汉字。
• 我不戴眼镜就看不清楚黑板上的汉字。

The second version is more compact and very natural in conversation.

Chinese frequently leaves out words that English would require, especially when the relationship between the two clauses is obvious.

Sometimes yes, if the context already makes it obvious who is being talked about.

For example, in conversation, someone might simply say:

• 不戴眼镜就看不清楚黑板上的汉字。

That can still mean I can’t see the Chinese characters on the blackboard clearly without glasses, if the speaker is clearly talking about themselves.

But including 我 makes the sentence clearer and more complete, especially for learners.

Because 眼镜 is the direct object of the verb 戴, and Chinese usually does not use a measure word in that position unless there is a number or demonstrative.

Compare:

• 我戴眼镜。 = I wear glasses.
• 我戴这副眼镜。 = I wear this pair of glasses.
• 我买了一副眼镜。 = I bought a pair of glasses.

So if you are just talking about glasses in general, 戴眼镜 is perfectly natural.

Although the pinyin is written bù, its tone changes before another fourth-tone syllable.

• 戴 is fourth tone: dài
• So 不戴 is pronounced bú dài

This is a common tone sandhi rule:

• 不 normally = fourth tone (bù)
• Before another fourth tone, it changes to second tone (bú)

So in this sentence, you would say:

• wǒ bú dài yǎnjìng jiù kànbuqīngchu hēibǎn shàng de hànzì

In careful pronunciation, the parts are:

• 看 = kàn (4th tone)
• 不 = bu here, often light and unstressed in the middle of the pattern
• 清 = qīng (1st tone)
• 楚 = chu or chǔ, depending on how carefully it is pronounced; in natural speech the second syllable of 清楚 is often lighter

So learners often hear something close to:

• kànbuqīngchu

The most important thing is to recognize the whole chunk as one common expression:

• 看清楚 = see clearly
• 看不清楚 = cannot see clearly

It is best to learn it as a unit rather than worrying too much about each syllable separately at first.

Yes, but the original order is very natural.

Original:

• 我不戴眼镜就看不清楚黑板上的汉字。

Possible variation:

• 我不戴眼镜的时候，看不清楚黑板上的汉字。
• 不戴眼镜，我就看不清楚黑板上的汉字。

Chinese often puts the condition first and then the result, which is exactly what happens here:

• condition: 我不戴眼镜
• result: 就看不清楚黑板上的汉字

That makes the sentence easy to process and very idiomatic.