Compel Truth

You compel a creature to tell the truth. The targeted creature must make a Charisma saving throw . On a failed save, a creature must answer one question truthfully or to the best of its knowledge. If the question is not worded carefully, a creature may choose to give a vague or misleading answer. 

At higher levels: When you cast this spell using a spell slot of 3rd level or higher, you can ask an additional question for each slot level above 2nd

An affected creature is aware of the spell once it has spoken the truth. If the spell fails the affected creature is aware the spell has been attempted on them and it cannot be attempted on the same target again with 24hrs.