Mat 26:50 Friend, wherefore have you come?
Alternative: Disciple, for what purpose are you here?

Christ knows why Judas has come as does everyone else present either because they are with Judas or because Jesus told them what was going to happen, so why does Christ ask? To make it clear that Judas's presence has a greater meaning than anyone there realizes.

Judas had his own motives: jealousy or greed or whatever, but from Christ's point of view, none of that matters. Just as Christ must go to his death to fulfill a larger plan, so much Judas betray him as part of a larger plan. It was important that a friend and disciple (the first word here) turns Christ over to the authorities. Why? Because ONLY a friend is able to turn on us and only a disciple can really turn on their beliefs.

However, there is a larger question here. Removed from the context, Christ is asking us all about our purpose. Why are we hear? Why are we present at this particular place an time? Christ's point is that there is a reason and purpose, an end (telos).

"Friend" is from hetairos (hetairos), which means "comrade," "companion," "pupil," "disciple," and "associate."

"Wherefore" is from epi hos, which literally means "on what."

"Come" is from pareimi (pareimi), which means "to be present," "to be near," and "to be ready."