1. I don't know who to say.

2. I don't know who to say about.
3. I don't know who I should say to.
4. I don't know who should say.
5. I don't know whom to say.
6. i don't know whom to say about.
(Which expressions are right?)

3 answers

when was robin hood born
#4 is correct. In that one "who" is the subject. You need "whom" when that is an object.

#5 could be: "I don't know whom to tell." Here you would tell something (direct object) to someone (indirect object)

Sra
First, Lidya, if you have a question, it is much better to put it in as a separate post in <Post a New Question> rather than attaching it to a previous question, where it is more likely to be overlooked.

As far as I know, Robin hood is a folklore hero rather than a real person. However, since this is not my area of expertise, I searched Google under the key words "Robin Hood birth" to get these possible sources:

http://www.britainunlimited.com/Biogs/Hood.htm
http://wiki.answers.com/Q/What_is_the_date_of_Robin_hood's_birth

In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search. Also see http://hanlib.sou.edu/searchtools/.

I hope this helps. Thanks for asking.