CIP Rules - How to deal with a double bonded nitrogen?
I have taken your functionality and I have incorporated it into structure 1 that has stereochemistry. The two double bonds in 1 are shown in the CIP shorthand of structure 2. C3 and C4 are non-duplicate atoms and they are attached to duplicate carbon atoms (4) and (3), respectively. Similarly, in the C=N double bond C1 is attached to the duplicate red nitrogen (N) while the non-duplicate red nitrogen is attached to duplicate carbon (1). Both non-duplicate and duplicate atoms of the same element have the same atomic number, however, duplicate atoms are attached to three phantom atoms of atomic number zero. In addition, all atoms (C,N,O,Cl,etc.) are treated as though they are quadrivalent.
In the digraph the blue numbers are the successive spheres emanating from the stereogenic center C2. In sphere 1 hydrogen has the lowest priority while C5 has the next lowest priority owing to the 3 H's in sphere 2. C1 is attached to N,(N),N in sphere 2, having the highest priority, while C3 is connected to 4,(4),H in sphere 2. The overall priorities are C1>C3>C5>H.
Now to the gist of your question. While N=N=(N), in sphere 3, (N) is attached to 0,0,0. (N) has the lowest priority of the three nitrogens. Of the remaining two nitrogens, C,C,0 = C,(1),0 in sphere 3 but this tie is broken in sphere 4 where H,H,H/H,H,H has priority over H,H,H/0,0,0. The nitrogen priorities are black N>red N>(N).