Between $N H_{3}$ and $N F_{3}, N F_{3}$ has greater dipole mough in $N H_{3}$ and $N F_{3}$ both, $N$ possesses one lone pair of electrons.

This is because in case of $N H_{3},$ the net $N$ - $H$ bond dipole is in the same direction as the direction of dipole of lone pair but in case of $N F_{3},$ the direction of net bond dipole of three- $N-F$ bonds is opposite than that of the dipole of the then lone pair.