I would say:

Could you please send me your mobile number.

I would regard could as more polite than can in this context. There is probably no proper way. All are grammatically correct.

Often (in American English) both phrases are used interchangeably, but in some contexts the second sentence, "Can you..." is used to determine a person's capability, rather than their willingness to do something.

A person in a loud bar might shout, "Can you hear me?"

Additionally, in some contexts "Would you..." is used to determine a person's willingness to do something without any expectation that the person will view the inquiry as a request. "Would you rather fight 100 duck sized horses, or 1 horse sized duck?"

In both of my examples, substitution would sound odd to a native American English speaker. Saying "Would you hear me?" or "Can you rather...?" will likely result in a confused look from your conversation partner.

Actually, sentences that begin with 'could', 'should', or 'would' are questions and should have a trailing question mark. Your original quote, "Could you please pass me the pepper shaker?", could be answered with a "yes" or "no." Although we usually use this syntax as a command it is not the same as the command "Pass me the pepper shaker," or "Please pass me the pepper shaker."

Etiquette tells us that it is more polite to ask for a response than it is to command a response.

“Could you” is more polite than “can you”. Regarding the rest of the wording, something about “tell me my next work” rings wrong to my ears. Probably, because you don't “tell a work”. So, maybe “tell me what my next work is?”. Finally, in most context, I'd use “job” instead of “work”, but that may be just me!

Examples, examples, examples. We all can come up with any number of perfectly on-topic questions beginning with either word at a moment's notice. A single word alone does not determine whether a question is on-topic or not, be it the first word in the title or any other word.

In fact, after just a quick check, 4 of the top 30 questions of my own begin with "is", and 6 of my top 30 answers are to questions that do likewise. That's 13% and 20%, respectively.

• Is it “despite” or “despite of”?
• Is it “alright” or “allright”?
• Isn't the word “uninstall” wrong?
• Is "rather" shifting to become a verb?
• Is there a subtle difference between “somebody” and “someone”, “anybody” and “anyone”?
• Is “not at all” still alive and doing well?
• Is there a word that contains all the vowels?
• Is the suffix “-ize” particularly productive in the morphological domain of nouns ending in “-nym”?
• Is there a word meaning “append”, but at the beginning, not the end?
• Is “my bad” a correct English phrase?

Nine out of these ten questions are open, and have 222 upvotes between them to boot. The top answers have 347 upvotes between them.

Similarly, 8 of the top 50 questions ever asked, or 16%, begin with "is", with hundreds upon hundreds upvotes between them:

• Is there a non-sexual phrase for sleeping with someone?
• Is there a correct gender-neutral, singular pronoun (“his” versus “her” versus “their”)?
• Is there a word or phrase for the feeling you get after looking at a word for too long?
• Is there a word for a person with only one head?
• Is there English counterpart(s) to Japanese old saying, “Present salt to your enemy.”?
• Is there a name for this type of sentence structure: “She looks as though she's been poured into her clothes, and forgot to say 'when'”?
• Is there an American English equivalent of the British idiom “carrying coals to Newcastle”?
• Is “believe you me” proper English?

And that's just a quick look at is. I am confident we can compile similar stats for questions beginning with can. Or do, which you haven't considered. (In fact, the two top answers on this site are both to questions beginning with do: Do most languages need more space than English and did English ever have a formal version of “you”.)

There is no denying some of these are MultiCollider bikeshedding flukes. But others are just as undeniably among the best this site has ever produced.

Most importantly, exactly none of these have received a simple yes/no answer, or would have been done justice receiving one and leaving it at that.

All that said, certain things — like not being able to spell "English" correctly on a site all about English, or titling your question "is this grammer??!!1" —, are certainly better indicators for poor or off-topic questions than others. But remember that even the poorest of questions can be saved by a great answer, possibly accompanied by an edit. And that's no hippie talk, that stuff actually happens. Indeed, the most recently introduced Explainer, Refiner, and Illuminator badges are right up that alley.

Conversely, there's no shame in admitting the greatest of questions can be shot down by a bunch of poor half-assed one-liners.

Anyway, I'd like to end this by saying that it'd be a nice, but fully surmountable, challenge, to edit every on-topic question on every SE site to begin with, end with, or include any word of your choosing. One word does not a swallow make. Don't get obsessed about symptoms, go after the malady.