Quote Originally Posted by tiudavidharris View Post
I have translated the following sentences. please correct me if there are errors.

'весь' means everyone or everything
я говорю за всё = i am speaking for everyone or everything
я говорю всем = i am speaking to everyone or everything

я говорю тебе = im telling to you
я говорю тебя = im telling you (this actually confusing me)

я спрашиваю за все = i am asking for everyone or everything
я спрашиваю всеx = i am asking to everyone or everything

do these following sentences mean anything? or are they nonsense?
я говорю на всё
я спрашиваю на всё
я спрашиваю всеx на столе
я спрашиваю всеx за столoм
You did not give enough context. Some combinations of prepositions and case can have some marginal senses (rare, colloquial, vernacular, slang etc.) in some specific situations. Native speaker can hardly remember all of them, but words come when they are needed.

я говорю тебя = im telling you (this actually confusing me) - this can confuse everybody. It means that "тебя" (in your phrase) is a phrase or a sentence or a speech - something that you can say out aloud.

я говорю за всё - 1. (Odessa funny accent, incorrect) I say about everything. 2. I am a representative of everything and I speak in the name of everything. (rather confusing sense)

я спрашиваю всеx на столе - "I am on the table (on the surface of the table) and asks everybody" or "I ask everybody, who is on the table..."

я говорю на всё: - 1) "I speak (by paid phone) long enough to spend all my money" 2) я говорю на всё: "ххх!" - I speak about everything (or in response to everything) : "xxx!".

я спрашиваю за все - "I demand answers for all bad deeds (and punish for all sins)"

etc. etc.

It is really bad idea to list ALL possibilities. It is a task for generations of native philologists.

P.S. It is Accusative, not Dative. Dative (всё - всему, все - всем) can not be combined with prepositions за and на.