Mutual inductance with open circuit, what's the voltage of the open circuit?
Since the secondary loop is open I2 must be 0


Of course it is - there is no current only an induced voltage. Because there is no current, the capacitor on the secondary side is effectively short circuit. And, because there is no current in the secondary there is no part-current flowing in the primary that is due to secondary current.

This boils down to a simple transformer problem where you need to find the voltage on L (primary) then knowing the coupling factor (aka M) you can calculate the secondary voltage.

Can you take it from here?