Consider a trio with nodes u, v, and w. The degree of the trio is just degree(u) + degree(v) + degree(w) - 6. The -6 comes from subtracting the edges u-v, u-w, and v-w, which are counted twice each in the vertex degree calculation.

To get the trios (u,v,w), you can iterate on u, then iterate on each w,v such that w and v are neighbors of u and are neighbors of each other.