The total number of $\pi$ electrons in the bicyclic ring system of indole (a benzene ring fused to a pyrrole ring, with N-H), counting the nitrogen lone pair that sits in a p orbital, is

Indole has four C=C bonds in its framework (three in the benzene ring and one more in the five-membered ring, the fusion bond being shared), which gives 8 pi electrons. The nitrogen lone pair in the p orbital adds 2, so the total is 10 pi electrons, $4n+2$ with $n=2$.