"I wonder if" sentences I was taught take periods at the end because they make a statement. These days, I often see "I wonder if" sentences end in question marks. Have standards changed on this matter? I'm wondering what is the correct handling of such sentences. Thank you.
There are two issues with the construction you mention. Let's start by creating a sample sentence. We'll work in third person because that's the standard for most kinds of fiction.
She wondered if this sentence would survive the red pen?
As written, I would want to correct this sentence. But I see two issues here, one of style and one of grammar. The grammar issue is a quickie, but it will help show the style issue for what it is.
Normally, to make a question in English, we do two things. We replace the period with a question mark, and we invert the main subject and verb. In our sample sentence, the main subject and verb are, "she wondered." Those are followed by a dependent adverb clause starting with the word "if." We don't invert the dependent part of the sentence. We invert the main subject and verb. So we would end up with:
Did she wonder if this sentence would survive the red pen?
That looks kind of bad, right? If we're in the pov of the "she" from this sentence, then she would know if she was wondering or not. The pov character's thoughts would not be hidden from the pov character. (Well, barring any plot elements involving mental derangement, experimental mind-bending drugs, and the like.)
You see, the real issue with this sentence lies not with the punctuation, but with the relegation of the important thought to a dependent clause attached to a "thought tag" type main clause. Thought tags attach to interior monologue the same way dialogue tags attach to dialogue.
She asked, "Will this sentence survive the red pen?"
She wondered if this sentence would survive the red pen.
In the dialogue, the tag serves to identify who asks the question. It's necessary to tag dialogue (or add a beat that identifies the speaker) when the speaker might not be otherwise clear. But if you're writing in an intimate point of view such as limited third, then the identity of the thinker ought to be known to the reader. The pov character can't think other people's thoughts. He can only think his own thoughts. So we don't need to attribute those thoughts if the pov is clear. And if that's the case, slice off that thought tag and move the dependent material into an independent clause of its own.
Will this sentence survive the red pen?
Now it's a proper question in terms of grammar, but it's also better fiction style.
Yes, there will be times you'll want to attach thought tags to the interior monologue because the nature or manner of thinking is important to the action. For example, if you're writing about a brain-trauma patient becoming capable of thinking again, then using those kinds of words -- he realized, he reasoned, he thought, he wondered, etc. -- at the moment when thought returns would be important to the text. But for ordinary circumstances, the fact of thinking is not critical to the plot, and so these kinds of words serve only to weigh the pacing and create narrative distance.