Is it better in general to translate нельзя as “саnnot”?

That really depends on the context. ‘Not allowed to’ is often OK, but not in this sentence. Because, well, how can you be allowed to know? It’s not something that can be forbidden, really, at least it Russian.

Also is there any way to differentiate “I cannot...” from “you cannot...” and “one cannot....”?

Yes, you can add the person who can’t be something in the dative-case form:

• мне нельзя́ ‘I can’t, I’m not allowed to’,
• тебе́ нельзя́ ‘you can’t, you’re not allowed to’ (informal singular),
• ей нельзя́ ‘she can’t, she’s not allowed to’,
• ему́ нельзя́ ‘he can’t, he’s not allowed to’,
• нам нельзя́ ‘we can’t, we are not allowed to’,
• вам нельзя́ ‘you can’t, you’re not allowed to’ (formal or plural),
• им нельзя́ ‘they can’t, they’re not allowed to’ (formal or plural),
• сестре́ нельзя ‘my sister can’t, is not allowed’.

Literally, «мне нельзя́» is like ‘to me, it’s not possible/allowed’.

"You cannot" is the closest working translation, fairly ambiguous about whether it is impossible, immoral, illegal or what. But it will always be a generic "you", i.e. it refers to people in general. This fact makes this translation both good and at the same time too vague. In English only context helps you understand the subtle difference between "You cannot speak Finnish", "You cannot outrun the arrow" and "You cannot piss onto people's doors". In Russian the first will never use нельзя, unless speaking Finnish has been outlawed recently.

If you have to express that someone is unable to to something or is not permitted to do something, there are other ways to do that.

• нельзя applied to a person is always about it being wrong rather than impossible (you should not do that).
• мочь is a verb that expresses ability to do something, used like any other verb (я могу, ты можешь etc.). Often used for one-time actions.
• уметь is a verb that expresses possessing a skill to do an action. Normally used with an imperfective verb (e.g. Он не умеет писать).
• other phrases also exist (e.g. "способен" or "в состоянии" than mean "able, capable")

If something is forbidden, запрещено or запрещается specifically expresses that (as you can imagine, that rarely comes up in speech). Their even more official versions are воспрещено and воспрещается (as in "Проход без предъявления пропуска строжайше воспрещается" ~ "Entry without demonstrating an ID is most strictly prohibited").

You can also use не разрешается and, maybe, не разрешено. Wait... you probably cannot but native speakers may do that in formal lists of rules (where "it is not allowed to do so-and-so")