The correct decreasing order of electron donating power of each nitrogen in the given compound is

a) Lone pair of electron localized, more available for donation

b) Lone pair of involved in resonance with benzene ring, less available for donation

c) Lone pair involved in resonance with $-\stackrel{\underset{\left|\right|}{\mathrm{O}}}{\mathrm{C}}-$ group -CO- group is more electron withdrawing as compared to benzene ring, least available for donation.

$\therefore$electron donating power of a > b > c.