My English textbook, Understanding Literature, is boring. My English textbook Understanding Literature is boring.
Robert Frost's poem, Mending Wall, is hard to understand. Robert Frost's poem Mending Wall is hard to understand.
My English textbook, Understanding Literature, is boring. My English textbook Understanding Literature is boring.
Robert Frost's poem, Mending Wall, is hard to understand. Robert Frost's poem Mending Wall is hard to understand.
This is a consideration that goes beyond book and poem titles. It's about appositives, i.e., a noun or noun phrase that serves to rename another noun. You English textbook and Understanding Literature are the same thing: the title just renames the thing that is your English textbook. The punctuation is matter of style, so you should consult your manual of style, either the one you've adopted or the one thrust upon you. The Chicago Manual of Style has appositives set off by commas:
We studied my favorite poet, Emily Dickinson, this year.
Unless the appositive is restrictive:
My granddaughter Emily is named after Emily Dickinson.
Since I have more than one granddaughter, the name is restrictive and isn't set off by commas.