The molecule contains two aromatic rings connected by an amide linkage. The ring attached to the nitrogen (anilide ring, bearing positions u and s) is activated towards electrophilic aromatic substitution because the nitrogen lone pair donates into the ring through resonance ($+M$ effect).

The other ring (carrying positions r and p) is attached through the electron-withdrawing carbonyl group ($-M$), which deactivates it.

Hence electrophilic substitution occurs predominantly on the anilide ring, at the para position labelled "u" (ortho/para to the $-NHCOPh$ activator, with para preferred for steric reasons).