Whether or not we agree? Do we agree?


At the end of a “suggestion letter”, what I should write?

1- Whether or not do we agree?
2- Whether or not we agree?

Or are they same?


I wouldn’t write either one, Tom. Neither one is a sentence and trying to use them as sentences sounds awful.
You could make a complete sentence this way, for example:
I’d like to know whether we agree.

Or you could write:

Please let me know whether you/we agree.

You don’t need to add “or not” because that is already understood.