The sentences should read:

1. Canadians feel they are a leading country in humanitarian aid.
   Canadians feel that Canada is a leading country in humanitarian aid.
2. When I reached the office, I discovered that I forgot my cell phone.
   When I reached the office, I discovered that I had forgotten my cell phone.
3. In reference to your letter dated January 6, 2001.
   I am writing a response to your letter dated January 6, 2001
4. Who do you want this memo sent to?
   To whom should I send this memo?
5. My associate really appreciates me helping him.
   My associate really appreciates my help.
6. Please call my secretary or myself by Friday.
   Please call my secretary or me by Friday.
7. All regional managers reports are due today.
   All regional managers’ reports are due today.
8. People usually get this answer wrong, irregardless of their grammar skills.
   People usually get this answer wrong, regardless of their grammar skills. 
9. If you make less than two mistakes on this test, you’re doing well.
   If you make fewer than two mistakes on this test, you’re doing well.
10. A group of employees are coming in to see you now.
    A group of employees is coming in to see you now.
11. Are these James file folders?
    Are these James’ file folders?
12. Anyone interested in improving their writing skills should take this course.
    People interested in improving their writing skills should take this course.