Speculate – To guess possible answers to a question when you do not have enough information to be certain
"The person with specs, you are late." (speculate) "Now you'll have to guess the answers to the quiz because you did not learn enough information to be certain."
Examples of speculate in a sentence
Unless you get a scan, you can only speculate which gender the baby will be.
I don't have to speculate, I know the butler murdered the king, I saw it.
It's not wise to speculate about problems in other peoples lives, we don't know what goes on behind closed doors.