Questioning is an appeal or demand for an answer, or for more information. Sometimes the police will bring a witness to a crime into the station for questioning.
When you participate in questioning, you may very well have a questioning look on your face. As an adjective, questioning can mean "curious," "confused or perplexed," or even "skeptical." If you show up at school in a clown costume, your teachers and friends might look at you in a questioning way — or they may dive right into the questioning, demanding: "What on earth are you wearing?"