Stu wrote:
Hello

Does anybody out there know what the prefix "?" means in combination with
i.e. a beacon symbol.

I don't know; there are certainly a number of underwater features that
are considered questionable, but its harder to imagine a beacon being
in the category, unless its privately maintained. Since many of us
have access to "charts of the world" it might help if you told us what
chart this is actually on, or at least which country and era. Also,
the full notation would be helpful.

Is this the right group to ask this kind of question? If not which one is
the right one?

It depends on what type of answer you want. rec.boats.cruising has a
larger number of folks who have done world wide cruising.