How to file these company names & the rules?
Aabar Books
ABCO Parts
Abbey, Joanne
AAA Auto Parts Co
Schmidt, J.B. Co
SOS Plumbing

It depends if you want to file by the literal name or the industry. What are the filing rules? E.g., is the company name Joanne Abbey?

File by literal name. Yes, Joanne Abbey is the company name.

File by literal name. Yes, Joanne Abbey is the company name.
Then that has to be under "J" as does "J.B. Schmidt Co."

Thanks! And what about the others company names in the first post?

Thanks! And what about the other company names in the first original post? Are you there?

If you are alphabetizing by company name, you keep the name intact --

Buster Brown Shoes (not Shoes, Buster Brown)
L.L. Bean (not Bean, L.L.)
Montgomery Wards (not Wards, Montgomery)
Sears, Roebuck & Co.
Warner Books (not Books, Warner)

Now, put your list in ABC order by company name.

AAA
Aabar
Abbey
ABCO
Schmidt
SOS
Is this correct?
My book says Aabar should be fourth.

AAA
Aabar
Abbey
ABCO
Schmidt
SOS
Is this correct?
My book says Aabar should be fourth.

What book ?

What you have listed is correct

AAA
Aabar
Abbey
ABCO
Schmidt
SOS
Is this correct?
My book says Aabar should be fourth.

Why Aabar fourth? What happened to JOANNE?

Passbook for Occupational Education Aide Civil Service Exam

Either you take advice of the experts, or you get off the board.

What book are you referring to ? It isn't a proper book for filing alphabetically.

Passbook for Occupational Education Aide Civil Service Exam

Filing rules are universal, or no one, absolutely no one could understand a system. Your reference means nothing unless you can file a link to what you are referring to.