What does Mark 9:16 mean?

We aren't told exactly what the scribes and disciples are arguing about, but it's not a unique event. Especially in the beginning of Jesus' ministry, the scribes and Pharisees tried to subvert His mission by casting doubt in His followers. When Jesus ate with tax collectors and other sinners, the religious leaders questioned the disciples (Mark 2:15–16). When the disciples ignored the extra-Scriptural customs on fasting and the Sabbath, the Pharisees confronted Jesus (Mark 2:18, 24; 7:5).

We also know that the scribes from Jerusalem claim Jesus' miraculous power came from Satan (Mark 3:22). Jesus later empowers the disciples to perform miracles of their own (Mark 6:7–13). So, when the scribes witness the disciples' unsuccessful attempts at exorcising a demon from a boy (Mark 9:18), the scribes apparently see their chance to assert their authority and try to draw the disciples back into their legalistic fold. It's likely that the scribes are insisting that the disciples cannot save the boy because they are not empowered by God.

The wording here is a bit confusing. We don't know whom Jesus is addressing. The other accounts (Matthew 17:14–20; Luke 9:37–43) aren't any help, as they dive directly into the father's plea. Whether Jesus is speaking to the scribes or the disciples, His question doesn't mean He doesn't know what is going on. Both He (Matthew 26:40) and God the Father (Genesis 3:9, 13) are known to use a question to take control of the situation and direct people's attention.