Au gets oxidised and Oxygen gets reduced.
Explanation:
4Au(s) + 8NaCN(aq) + O₂(g) + H₂O(l) → 4 Na[Au(CN)₂](aq) + 4 NaOH(aq)
Au is in 0 oxidation state is converted to an compound in that Au is in +2 oxidation state so it gets oxidised.
O₂, gets reduced from 0 to -1 oxidation state, so it also gets reduced.
Na and CN remains as such but with different atoms.