2 Cu(NO3)2 (aq) + 4 KI (aq) → 2 CuI (s) + I2 (s) + 4 KNO3 (aq)
This is an oxidation-reduction (redox) reaction:
2 CuII + 2 e- → 2 CuI (reduction)
2 I-I - 2 e- → 2 I0 (oxidation)
Cu(NO3)2 is an oxidizing agent, KI is a reducing agent.
This is a precipitation reaction: CuI andI2 is the formed precipitate.