4-Nitroaniline is diazotised with $\mathrm{NaNO}{}_2$ / dil. $\mathrm{HCl}$ at 273-278 K and the cold solution is added to alkaline 2-naphthol. The major product is

Diazotisation converts the amino group only; the nitro group stays, giving 4-nitrobenzenediazonium chloride. This coupling partner attacks 2-naphthoxide at C-1, giving 1-(4-nitrophenylazo)-2-naphthol. No reducing agent is present, so the nitro group is not changed to amino.