Hmm, I think the Thai translation for this sentence is a bit iffy for two reasons:
- The usage of a question mark character (?) in a Thai sentence isn't a common way to indicate a question
- The more common way to do it would be to add something like ไหม, หรือ or หรือเปล่า at the end of the sentence
- It's also not a very common thing to simply ask "A question mark?" in English, so that adds to the translation difficulty.
It then becomes a matter of what the speaker was trying to imply with the phrase.
- Person 1's Question: "What is this character?"
- Person 2's Answer: "(I'm not sure, is this thing) a question mark?"
In this case, I'd probably translate it to "เป็นเครื่องคำถามไหม"
Person 1 observes Person 2 write a sentence with a "?" character at the end, but Person 1 is doubtful whether that "?" character was suitable.
- Person 1 could ask Person 2 "(Are you really sure you needed to use) a question mark?"
In this case, I'd probably translate it to "เครื่องคำถามหรือ"