wǒ bú huì yòng, nǐ kěyǐ gěi wǒ kàn yíxià ma?

This is a tone change rule called tone sandhi.
不 is normally fourth tone: bù. But when it comes before another fourth-tone syllable, it changes to second tone: bú.

So:

• 不
  • 会 huì → 不会 bú huì

You will hear this very often, for example:

• 不是 → bú shì
• 不要 → bú yào

This is another common tone change rule, this time for 一.

一 is normally yī, but its tone often changes in connected speech:

• before a fourth-tone syllable, it becomes yí
• before a non-fourth-tone syllable, it usually becomes yì

Since 下 xià is fourth tone, 一下 is pronounced yíxià.

So the written character stays the same, but the pronunciation changes depending on what follows.

Here, 会 means know how to or be able to because of learned skill.

So 不会用 means:

• I don’t know how to use it
• I’m not able to use it because I haven’t learned how

This is different from other common modal verbs:

• 能 = can, be able to
• 可以 = may, can, be allowed to
• 会 = know how to, have learned to

In this sentence, 会 is the natural choice because using something is usually a learned skill.

Mandarin often leaves out objects when they are already clear from context.

So 我不会用 can mean:

• I don’t know how to use it
• I don’t know how to use this

And 给我看一下吗 can mean:

• Can you show me?
• Can you let me have a quick look?

If you want to be more explicit, you can add an object:

• 我不会用这个。
• 你可以给我看一下这个吗？

Leaving the object out is very normal when everyone already knows what is being talked about.

Here 给 does not literally mean give in the simple sense. In this pattern, 给 + person + verb means the action is directed to/for someone.

So 给我看一下 means something like:

• show me
• let me take a quick look

You can think of 给我 here as marking me as the person receiving the action.

This is a very common structure in spoken Mandarin.

一下 often softens the verb and makes the action sound brief, light, or less direct.

So:

• 看 = look
• 看一下 = take a quick look / have a look

In requests, 一下 makes the sentence sound more natural and polite. Compare:

• 你给我看。 → more direct, almost like a command
• 你给我看一下吗？ → much softer and friendlier

It does not always mean a literal one-time action. Very often, it is just a politeness softener.

Yes, 能 is also possible in many situations.

In this sentence:

• 你可以给我看一下吗？
• 你能给我看一下吗？

Both can work as Could you show me?

The difference is subtle:

• 可以 often relates to permission, possibility, or a polite request
• 能 often focuses more on ability or whether something is possible in the situation

In everyday conversation, both are common, and the difference is often small.
会 would not work as well here, because 会 usually means knowing how to do something as a skill.

吗 turns the sentence into a yes/no question.

Without 吗, this would sound like a statement:

• 你可以给我看一下。 = You can show me / Please show me a bit.
  (Depending on tone, it may sound like a statement or a suggestion.)

With 吗:

• 你可以给我看一下吗？ = Could you show me?

So 吗 is one of the most basic question markers in Mandarin.

This is a very important difference.

• 我不会用 = I don’t know how to use it
• 我不能用 = I can’t use it

But 不能用 can mean different things depending on context, such as:

• I’m not allowed to use it
• I’m unable to use it
• It can’t be used / it doesn’t work

So if you want to say you lack the skill or knowledge, 不会用 is the right choice.

Mandarin has its own fixed word order patterns, and 给 + person + verb is one common pattern.

So:

• 给我看一下 = show me / let me have a quick look

Putting 给我 after 看 would sound unnatural here.

A good way to remember it is that 给我 comes before the main verb to show who the action is for or directed toward.

Yes, it is already polite and natural in everyday speech.

If you want to make it even softer, you could say:

• 你可以给我看一下吗？
• 你能给我看一下吗？
• 麻烦你给我看一下，好吗？
• 可以请你给我看一下吗？

Adding 请 or 麻烦你 makes the request sound more courteous.

That said, the original sentence is already very normal and friendly.