The structure of melamine is :

Each nitrogen has one lone pair of electrons. Number (no.) of nitrogen in a molecule $=6$

Total no. of lone pairs in melamine

$$ \begin{aligned} & =\text { No. of nitrogen } \times \text { lone pair } \\\\ & =6 \times 1=6 \end{aligned} $$

Hence, total number of lone pair on nitrogen is 6.