Can't...

[Volcano1985]

"I can't know what you want exactly."

Using the "can't" here is wrong or doesn't make sense ?

[MrPedantic]

Hello Volcano

It probably means "it isn't possible for me to know exactly what you mean".

Do you have more context?

MrP

[curmudgeon]

"I can't know what you want exactly."

Using the "can't" here is wrong or doesn't make sense ?

It is wrong. I don't exactly know what you want.

I can't be expected to know exactly what you want.

I can't possibly know exactly what you want.

[MrPedantic]

Hello Volcano
It probably means "it isn't possible for me to know exactly what you mean".
Do you have more context?
MrP

(Sorry, I meant:

It probably means "it isn't possible for me to know exactly what you want".

MrP)

[Harry Smith]

"I can't know what you want exactly."

Using the "can't" here is wrong or doesn't make sense ?

It doesn't make sense. Maybe it's direct translation from your native language. Maybe you want to say "I can't understand what you exactly want" and another variant without "can't": I don't know what you want exactly.

[Volcano1985]

It doesn't make sense. Maybe it's direct translation from your native language. Maybe you want to say "I can't understand what you exactly want" and another variant without "can't": I don't know what you want exactly.

Yes its my native language translation.I should use "can't" if i want to give same meaning but "don't" is suitable too.

[Casiopea]

"I can't know what you want exactly."

Using the "can't" here is wrong or doesn't make sense ?

Volcano, if you change the verb from know to understand, then, yes, your assumption is correct. Both can't and don't work here:

Ex: I can't understand what you want, exactly.
Ex: I don't understand what you want, exactly.

They make sense.

The difference in meaning is very slight for some speakers.

- "can't understand" could mean, the person's pronunication or speech is making it difficult for you to make out what they are saying.

- "don't understand" could mean, the person's pronunciation and speech are clear, but you are having difficulty understanding their idea.

All the best.

[Volcano1985]

Volcano, if you change the verb from know to understand, then, yes, your assumption is correct. Both can't and don't work here:

Ex: I can't understand what you want, exactly.
Ex: I don't understand what you want, exactly.

All the best.

I have to use "know" here not "understand"

[Casiopea]

In that case, if you have to use know, then, can't doesn't work. It doesn't make sense. Sorry.

[riverkid]

"I can't know what you want exactly."
Using the "can't" here is wrong or doesn't make sense ?

It makes sense. Give it a context and it makes perfect sense.

But nevertheless, it tweaks some ENL' English meters.

[looking over a table of many different food dishes]

A: Get me a plate of food.

B: I can't [possibly] know what you want.

With the addition of "possibly", it sounds better.

Normally, we don't use 'can' to discuss a one time possibility. In English, 'can' is used to discuss general possibility.

A: Where's my pen?

B: ?? Kelly can have it. ??

We use 'could/may/might' for these situations.

B: Kelly could/may/might have it.

Does this extend to the negative, <can't>? I don't think it does in as strong a fashion but anyway, the negative wouldn't be the normal first response, so out of context it sounds unnaturaL. It's a strong negation, something that is more likely to come later, as in Scenario 2.

Scenario 1:

A: Where's my pen?

B: ? Kelly can't have it. ? [reads like a prohibition, not a measure of possibility]

Scenario 2:

A: Where's my pen?

B: Kelly probably has it.

C: Kelly can't have it.