1. In a letter with the following subject, do I have to capitalize certain words?
Request to remove "Unglowing" blog post regarding Obola
2. Is 'blog post' correct or should it be just 'blog'?
Without knowing any more context I can only say that you should ask for the "blog post" or "post" to be removed .. "blog" is short for "web log" and means the site itself, not just the posts on it.
If Obola is a person's name then it should be capitalised as you have it. If it's not a name, then I can't tell what it is or whether you need a capital.
not a teacher
Student or Learner