Yes, that is a grammatically correct phrase. You might use it as follows: I answer questions as well as possible.
Yes, "best possible" is correct grammar, as in this sentence: This is the best possible outcome considering the circumstances.
Both are possible and correct.
The sentence "It lacks agreement Possible correct alternatives are He is the one of the men who does the work or He is one of the men who do the work" are not of correct grammar.
I have worked with my mentor and responded to the customer
All is well
This is a correct grammar. But it is no possible to cash someone else's SS check.
No, "will be had" is not a correct grammar. The correct grammar would be "will have."
She plays very well is the correct way to say it.
No, the phrase "it is well" is not grammatically correct. It seems to be missing a verb or adjective to complete the sentence. You could say "It is well done" to make it grammatically correct.
No, it is correct grammar, not a correct grammar.
Well I think it is
The correct grammar is: "Are those correct?"